Acquired immunodeficiency syndrome virus
Constitution and life cycle of a virus of AIDS
The infection contamination a human immunodeficiency virus causing AIDS, is many-sided. In the beginning this virus usually intensively propagates, and free virions (virus particles) appear in fluid. A filling lumen head and a spinal cord, and as in a blood flow. The first wave of replication HIV can be accompanied by fever, an eruption, the phenomena, to similar symptoms of a flu, and sometimes neurologic disorders. Then for some weeks the quantity of the virus circulating in blood and cerebrospinal fluid, considerably decreases. Nevertheless the virus still is present at an organism. He can be found not only in Т-4 lymphocytes which in the beginning were considered as its unique target, but also in other cells of immune system, in cells of the excitatory system and an intestine, and as, most likely, in some cells of a spinal cord.
Here it makes sense to give the short description of that system of an organism which it puts out of action, that is immunodefence systems. It provides a constance of structure of proteins in our body and carries out struggle against an infection contamination and is cancerous regenerating cells of an organism.
As well as any other system, immune system has the organs and cells. Its organs are a thymus (thymic gland), an osteal brain, a lien, lymph nodes (them sometimes is irregular name lymphatic glands), a clump of cells in a drink, a thin intestine, a rectum. Cells of immune system are histic macrophages, monocytes and lymphocytes. The last in turn, are sectioned into T lymphocytes (their maturing descends in a thymus, whence and their name) and bursacytes (the cells maturing in an osteal brain).
Macrophages have diverse functions, they, for example, absorb bacteria, viruses and the blasted cells. Bursacytes develop immunoglobulins - specific antibodies against bacteriemic, virus and any other antigens - foreign high-molecular bonds. Macrophages and bursacytes provide humoral (from an armour. humor - fluid) immunodefence.
So-called cellular immunodefence is provided with T lymphocytes. Their type - T-killers are capable to blast cells against which antibodies were developed, or to kill foreign cells.
Complex and diverse reactions of immunodefence are regulated for the account of two more types of T lymphocytes: Т-helpers, designated also Т4, and a T suppressor, differently designated as Т8. The first suscitate reactions of the cellular immunodefence, the second oppress them. As a result neutralisation and excision of foreign proteins by antibodies, destruction of ingrained bacteria in an organism and viruses is provided, and also the cancerous regenerated cells of an organism, in other words, there is a harmonious development of immunodefence.
In general life cycle HIV, same, as at other viruses of this bunch. Retroviruses have received the name because in their development there is a stage on which information transmission descends in a direction anatropic to volume which is considered usual, normal. A genetical stuff of cells is DNA. During an expression of genes at first there is DNA transcriptional: it is formed copying it mRNA which then serves as a template for synthesis of proteins. As a genetical stuff of retroviruses serves RNA, and that there was an expression of genes, there should be DNA-copy of virus RNA. This DNA usual by provides synthesis of virus proteins.
Life cycle HIV begins that the virus particle joins outside a cell and introduces in it the core. The virion core contains two identical chains of RNA, and as structural proteins and the enzymes necessary at the subsequent stages of life cycle. Enzyme the anatropic transcriptase having some enzymatic activities, carries out stages of transmission of the genetical information of a virus - DNA synthesis. At the first stage it synthesises one-chained DNA on RNA, then disjoining last. Then the second is synthesised a chain, using the first in quality of a template.
The genetical information of a virus, already in the form of two-stranded DNA, inpours into a cellular kernel. With the help integrase activity of the same enzyme this DNA is built in chromosomal DNA. In such kind the virus DNA named a provirus, will be replicated together with own genes at division of a cell and to be transferred to following generations.
The second part of life cycle HIV - effecting of new virions - is made sporadically and only in some infested cells. It begins, when so-called long trailer repetitions (LTR; these are the special nucleotide sequences on the extremities of a virus genome) initiate a transcriptional of virus genes; thus the enzymes belonging to a host cell synthesise RNA - provirus repetitions.
Each virus particle collects from set of spears of two various albuminous moleculas which interrelation compounds approximately 20:1. The virion structure is simple enough and consists of two covers: choronomic - orbicular, and intrinsic - bullet. Last comprises two chains of RNA and enzymes: an anatropic transcriptase, a proteinase and an integrase. On a choronomic cover the squirrels which moleculas act from a membrane like thorns contain. Each thorn is formed by two or three identical subunits which in turn consist of two connected components representing glycoproteins. One component designated gp120 (a glycoprotein with molecular mass 120000), acts over a cell surface, and another - gp41 - like a hinge is dipped in a membrane. These glycoprotein complexes define ability HIV to infest new cells.
Smartly organised genetical regulators define, whether the virus round of replication and what will be intensity of reproduction will begin. Besides three genes for proteins of a core and a cover in genome HIV is available at least six genes. Some of them, and everything is possible also, regulate effecting of virus proteins: one gene provides an acceleration of synthesis of proteins in whole, another - only certain proteins, and the third - depressing of synthesis of proteins. As regulatory genes code the proteins, each of them influences not only structural genes, but also on regulatory genes, including on itself.
The regulatory gene tat (trans-activator of transcription) is responsible for flash of replication, which is observed, for example, in Т-4 cells, when they are activated at an occurring with an antigen (the foreign molecula causing the immune answer). The gene tat is unusual both on structure, and on the action. It consists of two nucleotide sequences located enough far apart. As a result of its transcriptional RNA (a primary transcript) which should undergo to a splicing (a mediate segment is formed cut out and coding sequences are bridged) that it has turned in mRNA and on it protein was synthesised. Protein influence - a gene product tat is very great: it can raise level of an expression of virus genes in 1000 times in comparison with that is observed at saltants HIV without this gene. The suscitating effect extends on all virus proteins - both on structural to a component of virions, and on regulatory proteins, including squirrels coded by a gene tat. Thanks to such positive feedback as soon as the mechanism with gene participation tat was activated, the large quantity of virus particles is very quickly formed.
While the gene tat enhances synthesis of all virus proteins without the analysis, the second regulatory gene, rev (regulator of virion-protein expression) possesses selective effect thanks to which are effected either regulatory squirrels, or virion components. Protein - a gene product rev, as well as in case of a gene tat, is coded by the separated nucleotide sequences which are bridged as a result of a RNA splicing. Two more sequences participate in regulation by this protein. One of them reacts as a represser: interferes with translation of transcripts which contain it. Other sequence co-operates with protein rev and takes out effect of the first sequence.
The sequence - a represser, named CRS (cis-acting repression sequence), is available in mRNA on which the squirrels forming virions - medullar squirrels are synthesised, enzymes of replication and coat protein; mRNA some regulatory proteins - products of genes tat and most rev - do not contain CRS. In absence of protein - a gene product rev - sequence CRS does not allow to collect long mRNA on which squirrels for virions are synthesised. On the contrary, short mRNA, coding regulatory squirrels not having CRS, are stable and are broadcast.
At protein presence - a gene product rev there is "relaying". This protein reacts on sequence CAR (cis-acting rev-responsive sequence) which too contains in long mRNA. It will thus be neutralised CRS and start to collect full-size mRNA, and instead of regulatory proteins squirrels from whom new virions collect are synthesised. Thus, the mechanism with gene participation rev can define transition from a masked infection to active reproduction of a virus.
However during replication interaction between mechanisms rev and tat can constrain virus reproduction, neutralise each other. The gene product tat enhances synthesis itself and the squirrel of a gene rev whereas the gene product rev slows down own synthesis and synthesis of protein coded by a gene tat. It is as a result established some kind of a homeostasis characterised by constant levels of proteins, coded by genes tat and rev, and moderate effecting of virus particles. The circumscribed replication allows a virus to be replicated by years, not killing infested cells, therefore such type of genetical regulation can be an adaptive sign of the retroviruses which masters are kinds with long time of life, such as the human.
Besides the activator (tat) and a selective regulator (rev) at HIV there is a negative regulator. Which slows down a transcriptional of a virus genome. The gene of the negative regulatory factor designated nef (from English negative-regulatory factor), probably, defines ability HIV to stop reproduction and to pass in a rest condition.
The sequence which is a target the squirrel - a gene product nef, is located in the beginning of a virus genome in long trailer repetition. It is called as a negative regulatory element (NRE, from English negative - regulatory element). NRE depresses a transcriptional even in itself; if virus LTR, deprived of this sequence to introduce into not infested cell, it provides the raised level of a transcriptional of cellular genes. The gene product nef enhances effect NRE. But how it reaches it is a riddle.
Complex mechanisms of regulation of reproduction HIV react not in isolation: they are closely bound to a host cell metabolism. To begin that the virus uses the cellular apparatus for a transcriptional of the genes and synthesis of proteins. In particular, cellular factors obviously play a role in flash of replication HIV descending with the assistance of a gene tat when the infested T-cage is suscitated by an antigen. Features of molecular "climate" of a host cell also, possibly, somehow influence rate of reproduction of a virus which is various in various types of a cell.
Probably, for communication of cellular and virus processes communication of cellular proteins with LTR in the beginning of a virus genome matters. Sequences in LTR define a site of an initiation of a transcriptional of virus genes - a starting point in which synthesis mRNA begins. At least eight proteins which in norm participate in a cellular transcriptional, contact cellular DNA in a site of an initiation of a transcriptional or near to it. They play a part in the course of a transcriptional. One of proteins which learns initiatory sequences, plays a specific role in T-cages and other lymphocytes. This protein is activated, when the lymphocyte is suscitated by antigens and starts to propagate. It is considered, that it promotes cell reproduction, enhancing a transcriptional. As it was found out, at stimulation of infested T-cages linkage of this protein with a provirus genome strengthens. Thus activation of this protein can be one of pathes of an acceleration of reproduction HIV at T-cage stimulation.
Possibly, the panel of cellular factors reacting on a virus genome, varies in dependence both on conditions, and on a host cell type. Some cells, being in a rest condition. Can simply not have some the proteins necessary for initialization of a transcriptional so the infection contamination remains hidden. In other cells rate of reproduction of a virus can be circumscribed because of low concentration initiatory factors or because of excess of the proteins inhibiting synthesis mRNA. Thus, the host cell by means of own factors of a transcriptional frames the molecular environment influencing regulatory mechanisms HIV.
After as a result of action described above mechanisms effecting of virus particles has begun, game is entered by last gene. This gene named vif (from English virion infectivity factor - the factor of an infectivity of a virion), codes the small protein which is found in a cytoplasma of infested cells and round them in intercellular medium and as in free virus particles. Protein - a gene product vif somehow enhances ability of the gemmated virion to infest other cells. At strains HIV with the mutations inactivating vif, virions have a normal appearance, contain a full panel of RNA and enzymes, but infest cells much less effectively.
Stages of infestation of a cell AIDS virus
The first step of any virus infection contamination - linkage of a virus particle with a component of a membrane of an infested cell. For HIV the role of such receptor component plays the protein named antigen CD4. (The Antigen is a molecular structure which is learnt by an antibody.) from this follows, that allocation CD4 in an organism should correspond to tropism HIV, i.e. a spectrum of cells and the tissues amazed with a virus. Antigen CD4 meets mainly on the lymphocytes named Т-4 helpers which are the important element of immune system and as on some other cells.
As it has been established, linkage descends, if CD4 co-operates with virus coat protein gp120 which is distributed on a choronomic surface of a membrane. It was possible to define specific fragments of moleculas CD4 and gp120, participating in linkage. These results discover possibility of double struggle with HIV: to interfere with interaction of a virus with cellular receptor CD4 it is possible quenching a receptor or shielding the virus protein gp120.
Owing to a lesion of the blood cells carrying antigen CD4, especially Т-4 lymphocytes, on its concentration it is possible to judge infection rate AIDS. In cellular cultures it is possible as to observe one more sign of infestation rather convenient for research - formation of multinuclear sincytia. The sincytium represents the colossal cell containing set of kernels in one membrane. It is formed as a result of the cell fusion, infested HIV, with the healthy cells carrying moleculas of a receptor.
The most strict proof of such mechanism of interaction of a virus with a cell there was an experiment spent to 1984 at the Colombian university of the USA. It was possible to tolerate a gene coding CD4, to cells HeLa - a line of cells of a cancer tumour of a neck of a uterus. These cells do not contain CD4 and in norm are not infested HIV. Whereas the variated cells HeLa carrying CD4, can be infested HIV then they quickly merge in huge sincytia.
This experiment has given, besides, one unexpected result which completely is not explained till now. Human gene CD4 has been introduced into murine T-cages which thereby have got ability to effect the conforming protein. Particles HIV contacted these variated cells, however infection contamination signs were not: it was not formed neither a sincytium, nor infectious virus particles. It was surprising, as murine cells are generally capable to sustain reproduction HIV under some conditions. Most likely, murine cells cannot be infested by particles HIV even in the presence of receptors HIV. To infestation of murine cells have appeared also some related viruses are incapable. These facts allow to assume, that any component of a cellular surface that a virus attached to a cellular membrane a smog inpour in a cell is necessary still. The nature of such accessory factor is not clear yet.
Linkage virus gp120 with cellular CD4 is only the first stage of penetration of a virus in a cell. The subsequent stages while are less clear. For example, how the virus genetical stuff gets to a cell? The elementary and most probable possibility consists that the virion cover merges with a cellular membrane and contents of a virus particle (including a genetical stuff) appear in a cell. Other possible path - endocytosis, i.e. formation of a small invagination of a cellular membrane which then gemmates inside, turning to the closed membranous blister. The blister completely surrounds a virus particle and tolerates it in a cell. There the membrane forming a blister (now it is called as an endosome), is oxidised. It leads to conformational changes, its coalescence to a virus membrane and remission of contents of a virus particle in intracellular space.
Regardless of the fact that actually descends - direct coalescence or endocytosis - the virus membrane should undergo coalescence to the cellular. How it is carried out? According to one of the hypotheses, represented quite plausible, linkage gp120 with CD4 causes change of conformstion of protein gp120 owing to what the part of other coat protein is bared, gp41, in norm hidden under a molecula gp120. This range gp41 hydrophobic and consequently should take root into a membrane, instead of remain outside, in water medium, pericellular. Having appeared open, the hydrophobic range gp41 co-operates with a nearby part of a cellular membrane and induces its coalescence to a virus membrane. It is not clear yet, whether any receptor of a cellular surface, besides CD4 is necessary for linkage with gp41 still, or gp41 itself takes root directly into a cellular membrane.
After HIV has inpoured on cellular medium and its genetical stuff it was integrated into a cellular genome, it can remain inactive and in any way itself not find, and can and show one of three means.
First, the virus genome can cause a persistent infection contamination; a quantity of virus particles is thus formed, but cells perishes a little. Secondly, the infection contamination can lead to formation of a sincytium which soon perishes. Appearance of sincytia - the main result of influence HIV on culture of cells. In an organism of the infested human sincytia sometimes can be observed at serotinal stages of an infection contamination (especially in a brain). Whether they obscurely, however, play any role in an early pathogenesis of AIDS.
The third probable result of infestation HIV - fast destruction of cells without formation of sincytia. How HIV kills cells it is not clear yet. Probably, any of the products coded by genes HIV, possess direct toxic action. Probably, also destruction of cellular membranous system of that taken root into it gp120, synthesised as a result of an infection contamination, co-operates with available in membrane CD4. The destiny of an infested cell depends and on the immune answer as the immune system is capable to learn virus proteins on a surface of infested cells and to kill these cells.
Allocation infested HIV cells in an organism is caused mainly by how the cells carrying CD4 are distributed. Initially this antigen has been identified on its presence on certain T lymphocytes. And it is valid, its normal functions, apparently, basically are bound to a complex network of interactions between cells of immune system.
The T lymphocytes carrying CD4, are capable to co-operate with the cells representing antigens. These last find foreign antigens and exhibit them on the cellular membrane together with specific squirrels - glycoproteins MHC of a class II (from English Major Histocompatibility Complex - the main complex of a histocompatibility). When Т4-хелперы learn a combination of an antigen and glycoprotein MHC of a class II, they initiate the immune answer against the foreign or infested cells carrying this antigen. It is considered, that interaction between antigens CD4 on T-cages and glycoproteins MHC of a class II on the cells representing an antigen, the important element of contact of these cells.
As now it is known, T lymphocytes not unique cells with antigen CD4 built in a membrane. Not less than 40 % of monocytes of peripheric blood (these cells are precursors of macrophages - cells - of "ashmen") and some cells representing an antigen in lymph nodes, a skin and other organs, and also approximately 5 % of all V-cages of an organism (these cells effect antibodies) carry CD4 and can be infested HIV.
But some kinds of cells are infested HIV in culture, and directly to secure in them CD4 it is not possible. Glial cells of a brain, a cell concern them of some cancerous tumours of a brain, and also certain lines of cells from cancer tumours of an intestine. However, though these cells also do not effect CD4 in experimentally definable quantities, they contain a little the information RNA coding squirrels CD4 so, are capable to synthesise and itself CD4. Apparently, it is enough for infestation HIV even very small quantity CD4.
The preparations resisting to AIDS
Any therapeutic agent against an infection contamination irrespective of the pathogen nature - whether it be a virus, a bacterium, a fungus or the elementary - should or cause destruction of pathogen, or stop its reproduction. Thus the preparation should not cause essential harm to an infested organism. As a rule, such medicines carry out the problem, reacting on biochemical processes, characteristic only for pathogen. In case of bacteria it is reached rather simply as on structure and a metabolism of a cell of bacteria and cells of an organism of a mammal strongly differ. For example, Penicillinum breaks synthesis of a cellular side of bacteria, and on cells of mammals which do not have such side, it does not react.
With viruses a situation is much more complex. Viruses represent simply genetical stuff dressed in a cover from glycoproteins and lipids. They are not capable to propagate independently and instead infest cells of other organism and usurp their apparatus of biosynthesis which provides virus reproduction. When there is an active replication of a virus, often happens difficultly to distinguish the virus proteins co-operating with a cell and the squirrel of the cell. The close connection of many stages of life cycle of a virus with a host cell metabolism complicates building of preparations which selectively depress replication of a virus and during too time is minimum influence a cell.
Essential also, that practically any preparation (including Penicillinum) possesses to some extent a side effect and toxicity. Therefore always it is necessary to consider not only effect of influence on pathogen, but also the harm caused to a human body. The major characteristic of a potential therapeutic preparation is it “the therapeutic index”: the attitude of a toxic dose to an effective dose. However in case of the diseases representing threat for life, such as AIDS, is admissible to use and preparations with rather low value of a therapeutic index at least, are not framed yet more perfect.
Complex life cycle allows HIV to infest cells of immune system and to escape their action. But for struggle against an infection contamination such complexity can be not only disaster, but also the blessing as it gives many possibilities for influence of antiviral agents.
The first stage - linkage of a virus with a cell (see above). There are some possibilities to depress this process. It is possible to receive antibodies which co-operate with the conforming part of a cover of a virus and by that will neutralise ability gp120 to contact CD4. It is possible to bridge such antibodies to moleculas of any toxin then they, contacting infested cells, for example with macrophages, viruliferous and effecting its proteins, will kill them. It is possible to receive and antibodies to CD4, but this approach is potentially dangerous, because such antibodies will attack also healthy cells of immune system of an organism. Therefore researches are referred mainly on reception of antibodies to gp120.
To receive effective antibodies, neutralised gp120, for some reasons it is difficult. Not all antibodies against gp120 will quench a key binding site with CD4. At patients, in which organism in the course of normal reaction to infection contamination HIV neutralised antibodies are formed (usually only in small quantity), AIDS nevertheless educes. The certain permission of this problem while is not present. Probably one of the causes - high rate mutating HIV. At some variants of a virus arising in an organism the cover glycoprotein can be variated, and it will not neutralise available antibodies. The second possible cause consists that moleculas of Saccharums. Covers HIV a part of a glycoprotein, are similar to similar structures on a surface of cells of the human, therefore on a cover of a virus not enough unique fields which will be distinguished by immune system as "strangers" and to which antibodies could be bound. Thirdly, in moleculas gp120 binding site CD4 is located in an excavation and consequently is a little accessible. At last, it is not excluded, that the important fields for linkage gp120 are open only at the moment of linkage, and time most part are inaccessible to immune system.
To overcome these difficulties some approaches are applied. One consists in reception of monoclones. For this purpose it is necessary to identify antibodies which really contact a key field of virus protein, to clone lymphocytes effecting them and to grow up these cells in vitro.
The second approach uses anti-antiself antibodies, i.e. “antibodies against an idiotype”; in this case it is antibodies against antibodies to CD4. The idea consists that the molecula of a monoclonal body against CD4 on structure can imitate binding site CD4 in a molecula gp120 and consequently the antibody (antiidiotype) to this field should contact gp120.
The third approach consists in building solvable, i.e. form CD4 not bound to cells which is capable to co-operate with HIV, occupying its binding sites and by that interfering with its linkage with CD4 on surface Т4-хелперов. Now solvable CD4 has been received by gene engineering methods. This preparation really quenches binding sites CD4 on cover HIV and depresses infestation of T-cages. Possibly, it will be difficult to virus to variate so that to lose affinity to CD4, keeping thus ability to infest other cells.
In the future, probably, the constant part of a molecula of an immunoglobulin of the human will be possible to frame "chimaira" moleculas in which will be united the field of molecula CD4 co-operating with HIV, and. Such antibodies "to order" should possess a number of advantages. Certain fields of heavy chains of an immunoglobulin are capable to activate other components of immune system, leading to virus destruction. The chimaira molecula would react like the policeman with a police dog: part CD4 will track down a virus, and an immunoglobulin part - to cause help for an offence. Besides, chimaira moleculas can be more longly in a blood channel, than simply solvable CD4 because certain immunoglobulins possess big time of life in a blood flow.
At the heart of the surveyed approaches use of complex biological moleculas which contact a superficial glycoprotein of a virus lays. However with a similar mode can react and other moleculas. It has been shown, that some large negatively charged bonds keeping sulphatic bunches, depress replication HIV. As a prototype the dextran sulphate which moleculas with molecular mass within 7000 - 8000 dalton depress replication HIV in vitro can serve. One of mechanisms of action of a dextran sulphate, possibly, is depressing of linkage of a virus. It is established also, that this bond in vitro stirs to formation of sincytia that can be expected for the agent quenching linkage of a virus. However, toxic and effective doses of this preparation while are insufficiently studied.
When HIV has contacted a cell, the virus membrane merges with a cellular membrane, and virion contents get to a cytoplasma. Here its medullar squirrels particulate leave, baring RNA. Antibodies to gp41 could prevent penetration of a virus into a cell. "Undressing" of RNA interfering process is possible also a reagent.
However as a target for influence on a virus the greatest attention was involved in itself with the following stage of life cycle of a virus - synthesis of virus DNA by an anatropic transcriptase. The special advantages as this stage is characteristic only for a retro of viruses Here see and does not concern a host cell. In search of antiretroviral agents the paramount attention to this problem was from the very beginning paid. In particular the bonds named dideoxynucleosides which are inhibitors of an anatropic transcriptase were investigated. These are analogues of nucleosides, i.e. on structure they are very close to the nucleotides serving by monomers of DNA and RNA.
One of such bonds - 3 `-azido-2 `, 3 ` - a dideoxythymidine, or an azidothymidine. It has been synthesised in 1964 and pristinely designed as an anticancerogenic preparation. In 1985 it was revealed, that it is a powerful inhibitor of reproduction HIV in culture of T lymphocytes in concentrations 1 - 5 microns (0,25 - 1,25 mkg/ml). Thus it was not observed appreciable toxicity of an azidothymidine at concentrations 20 - 50 microns or less. It has soon been shown, that the azidothymidine effectively reacts at sick of AIDS at concentration in an organism 1 - 5 microns, as well as was predicted on the basis of research in culture of T-cages.
How this bond protects cells from HIV? The short consists that it is close on structure to a nucleoside to a thymidine which is a part of DNA. In a cell the azidothymidine is exposed enzymatic phosphorylation: the chain of three phosphatic bunches joins it. The azidothymidine triphosphate also is the active form of a preparation. (To introduce into an organism immediately an azidothymidine triphosphate it is impossible, as cells are not capable it to absorb.) an azidothymidine triphosphate is analogue a triphosphate thymidine - one of DNA monomers. Apparently, the mechanism of depressing of synthesis of virus DNA the double: competitive inhibition and termination of synthesis of a chain of DNA.
Competitive inhibition consists that an azidothymidine triphosphate contacts an anatropic transcriptase in that field which in norm binds usual a nucleoside triphosphates. At termination of synthesis of a chain of DNA the anatropic transcriptase wrongly includes an azidothymidine triphosphate in growing a chain of virus DNA instead of a triphosphate thymidine, but apposition of a following nucleotide is impossible, because in a molecula the azidothymidine of triphosphate is not present hydroxylic bunch which is necessary for formation of communication with a following nucleotide. A virus not in a condition to rectify this error and synthesis a deck stops.
Other dideoxynucleosides possessing activity against HIV, react, apparently, in the same way. All these bonds have appeared effective against a number of retroviruses (actually all which were studied on this subject), but only in the form of triphosphates. Therefore their efficacyy as therapeutic agents is defined by that, how much easily they inpour into cells and phosphorylate the cellular enzymes named kinases. For example, phosphorylate one dideoxynucleosides descends better, than others. So 2 `, 3 ` - the dideoxythymidine which differs from an azidothymidine that instead of azido group (N3) there is an atom of hydrogen, in cells of the human badly phosphorylation and consequently is less effective against HIV, than an azidothymidine. Besides, process phosphorylation these bonds differs at different kinds so models on animals can be inadequate for a prediction of efficacyy concrete dideoxynucleotide in a human body.
It is very important, whether the anatropic transcriptase of a virus as a result of mutations can variate in such a manner that will not be inhibited any more by an azidothymidine. It is a question not so idle. The azidothymidine is effective so far as as anatropic transcriptase HIV prefers an azidothymidine triphosphate a thymidine to triphosphate, binds it and includes in DNA while DNA-polimerazy of cells of mammals do not possess such affinity to an azidothymidine to triphosphate, synthesis of cellular DNA is not broken also a cell continues to function successfully. It is not excluded, that the anatropic transcriptase could lose preference to an azidothymidine to triphosphate.
After on virus RNA it was synthesised DNA chain, the second stage of process of reverse transcription - synthesis of the second strand of DNA, complementary begins the first. At this stage action of medicinal preparations also is possible. For example, it is possible to try to break work of the virus enzyme RNase H which is a part of an anatropic transcriptase; RNase H after the first strand of DNA is synthesised, disjoins virus RNA, releasing thereby a place for formation of the second strand. Probably, it will be possible to quench and other part of enzyme - an integrase which as believe, cuts DNA of a host cell and inserts into a breakage of DNA of a virus.
The weak spot following potentially in cycle HIV appears a little bit later when the host cell is activated. The cell can start to synthesise new proteins and also to share. The same process which activates a cell, can initiate a transcriptional of a provirus and translation with formation of virus proteins. There is a possibility to break this process, using “antisemantic oligonucleotides”. The short of this idea consists in the following. It is necessary to receive oligonucleotides (short sequences of nucleotides), complementary parts virus mRNA; mRNA is a semantic sequence as it immediately codes squirrels, and oligonucleotides are called as antisemantic because they are complementary mRNA. These nucleotides are capable to contact virus mRNA; descend, as speak, molecular hybridization: the duplex is formed, i.e. The two-stranded field of a molecula which, possibly, interferes with locomotion of ribosomes of a cell along virus mRNA and by that quenches synthesis of virus proteins. Such mechanism is called as the hybridization block of translation.
As a medicine oligonucleotides are bad that many of them can be disjoined in cells under the influence of enzymes. The truth they can be made steady against a zymolysis if to modify defined phosphodiester bonds between nucleotides.
Basically probably to prevent formation of virus particles, quenching genes or proteins who carry out regulation of replication HIV.
Besides, squirrels of the cell can influence replication HIV and even viruses which have casually infested the same cell. For example, it has been shown, that cellular protein NF-kB which plays a role of an intracellular signal of activation in some lymphocytes, is capable to initiate replication HIV. At infestation by a number of Herpesviruses in a cell the protein known under name ICPO which also can be the initiator of replication HIV are formed. Therefore at the patients infested simultaneously both HIV and Herpesviruse, probably, it will be possible to detain AIDS development, supervising herpes an infection contamination, for example, by means of an aciclovir preparation.
Now explorers do not need to pin the hopes on any one method of treatment or a medicinal preparation - opposite, it is necessary to use the best efforts to develop set of various agents, capable to attack HIV at various stages of its life cycle. Experience of studying of an azidothymidine will serve good service at "finishing" of preparations to a stage when they can be used for treatment of patients. Since that moment as activity of an azidothymidine against HIV to the statement of a preparation for application in medical practice has been found has passed about two years. Undoubtedly, so the rapid progress speaks careful, scientifically reasonably clinical tests. It is difficult to overestimate value of a test method with control bunch - as for success of the future agents of treatment of AIDS, and for studying of this disease as a whole without what the victory over it is inconceivable.
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