Reverse transcriptase

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Being the protein that gives their name to Retroviruses, Reverse Transcriptase is, in company of Protease and Integrase, the most important part of the protein system involved in the process of infection of viruses like HIV, MuLV and AMV, and has the unusual property of transcribing ssRNA into dsDNA going against the Central Dogma of Molecular Biology. Since its discovery in 1970, the study of its properties and mechanisms of action have been of high interest among the scientific community due to the unique properties that makes it an important medical target enzyme and important tool for genetic engineering applications like RT-PCR in the construction of cDNA libraries.

StructureStructure

This hand-like protein that has an usual length of 1000 residues (560 in Chain A and 440 for B), the third of them involved in alpha helical and almost a quarter in beta sheets, showing α+β domains; has an usual weight of 66KDa whereas is around 51KDa, those monomers are derived from the same gen but p51 lacks the aminoacids of one active site and has a different tertiary structure conformation compared with p66, for this reason is totally inactive. [1]

FunctionFunction

As a RNA-dependent DNA Polymerase, is able to recognize the initial RNA, transcribe it to ssDNA, cleave the remaining RNA and then build up the dsDNA, to do this the protein has two active catalytic zones. Chain A has the that consist of two finger-like domains, one of them recognizes the initial nucleic acid by h-bonds interactions with phosphate groups of the side chains, then both domains make a conformational change closing the recognition hole to allow the second domain with the support a coordination system, begin the transcription process adding the specific DNA nucleotides; this change is allowed by a between the two previous domains that is used as a common pharmaceutical target site in order to prevent this change and by this way inhibit the activity, but this one is the only zone of the Chain A that has non-conserved aminoacids giving the virus more drug resistance. [2] As the same rate that the polymerization process occurs, the other active site known as the , cleaves the RNA releasing the ssDNA that comes again trough the Polymerase active site to become dsDNA (all this with a coordinative system, that allows non-specific recognition, just with phosphates). Finally Chain B despite of the similar aminoacid sequence with Chain A has no enzyme activity, possibly its function is to stabilize and communicate both active sites, this varying the length between them in order to synchronize both functions. This seems to be the most general idea of the mechanism of action of Reverse Transcriptase, however the process remains unclear and new approaches are being reported. [3]

One of the principal issues about this protein comparative with the usual DNA polymerase (besides to the similarity with the Klenow fragment), is the lack of a correction mechanism (usually made by DNA PolIII in the DNA Polymerase) that increase the quota of errors, producing more mutations and by this way giving more facultative and resistance abilities to the virus.

See AlsoSee Also

• Reverse Transcriptase at Wikipedia
• Molecule of the Month (09/2002) at RCSB Protein Data Bank
• List of Reverse Transcriptase articles at Proteopedia and at RCSB Protein Data Bank
• of Reverse Transcriptase as one of the CBI Molecules on the Molecular Playground

ReferencesReferences

• [1] Kohistaedt, L.A. et al. Science. 256, 1783-1790 (1992) | doi:10.1126/science.1377403
• [2] Consurf Server Data Base. Evolutionary conservation profile for Reverse Transcriptase PDB file 1JLB
• [3] Abbondanzieri, E.A. et al. Nature 453, 184-189 (2008) | doi:10.1038/nature06941