Structural highlights
Function
[POL_MLVMS] Gag-Pol polyprotein plays a role in budding and is processed by the viral protease during virion maturation outside the cell. During budding, it recruits, in a PPXY-dependent or independent manner, Nedd4-like ubiquitin ligases that conjugate ubiquitin molecules to Gag, or to Gag binding host factors. Interaction with HECT ubiquitin ligases probably link the viral protein to the host ESCRT pathway and facilitate release. Matrix protein p15 targets Gag and gag-pol polyproteins to the plasma membrane via a multipartite membrane binding signal, that includes its myristoylated N-terminus. Also mediates nuclear localization of the preintegration complex (By similarity). Capsid protein p30 forms the spherical core of the virion that encapsulates the genomic RNA-nucleocapsid complex (By similarity). Nucleocapsid protein p10 is involved in the packaging and encapsidation of two copies of the genome. Binds with high affinity to conserved UCUG elements within the packaging signal, located near the 5'-end of the genome. This binding is dependent on genome dimerization. The aspartyl protease mediates proteolytic cleavages of Gag and Gag-Pol polyproteins during or shortly after the release of the virion from the plasma membrane. Cleavages take place as an ordered, step-wise cascade to yield mature proteins. This process is called maturation. Displays maximal activity during the budding process just prior to particle release from the cell (By similarity). Reverse transcriptase/ribonuclease H (RT) is a multifunctional enzyme that converts the viral dimeric RNA genome into dsDNA in the cytoplasm, shortly after virus entry into the cell. This enzyme displays a DNA polymerase activity that can copy either DNA or RNA templates, and a ribonuclease H (RNase H) activity that cleaves the RNA strand of RNA-DNA heteroduplexes in a partially processive 3' to 5' endonucleasic mode. Conversion of viral genomic RNA into dsDNA requires many steps. A tRNA binds to the primer-binding site (PBS) situated at the 5' end of the viral RNA. RT uses the 3' end of the tRNA primer to perform a short round of RNA-dependent minus-strand DNA synthesis. The reading proceeds through the U5 region and ends after the repeated (R) region which is present at both ends of viral RNA. The portion of the RNA-DNA heteroduplex is digested by the RNase H, resulting in a ssDNA product attached to the tRNA primer. This ssDNA/tRNA hybridizes with the identical R region situated at the 3' end of viral RNA. This template exchange, known as minus-strand DNA strong stop transfer, can be either intra- or intermolecular. RT uses the 3' end of this newly synthesized short ssDNA to perform the RNA-dependent minus-strand DNA synthesis of the whole template. RNase H digests the RNA template except for a polypurine tract (PPT) situated at the 5' end of the genome. It is not clear if both polymerase and RNase H activities are simultaneous. RNase H probably can proceed both in a polymerase-dependent (RNA cut into small fragments by the same RT performing DNA synthesis) and a polymerase-independent mode (cleavage of remaining RNA fragments by free RTs). Secondly, RT performs DNA-directed plus-strand DNA synthesis using the PPT that has not been removed by RNase H as primers. PPT and tRNA primers are then removed by RNase H. The 3' and 5' ssDNA PBS regions hybridize to form a circular dsDNA intermediate. Strand displacement synthesis by RT to the PBS and PPT ends produces a blunt ended, linear dsDNA copy of the viral genome that includes long terminal repeats (LTRs) at both ends (By similarity). Integrase catalyzes viral DNA integration into the host chromosome, by performing a series of DNA cutting and joining reactions. This enzyme activity takes place after virion entry into a cell and reverse transcription of the RNA genome in dsDNA. The first step in the integration process is 3' processing. This step requires a complex comprising the viral genome, matrix protein and integrase. This complex is called the pre-integration complex (PIC). The integrase protein removes 2 nucleotides from each 3' end of the viral DNA, leaving recessed CA OH's at the 3' ends. In the second step that requires cell division, the PIC enters cell nucleus. In the third step, termed strand transfer, the integrase protein joins the previously processed 3' ends to the 5' ends of strands of target cellular DNA at the site of integration. The last step is viral DNA integration into host chromosome (By similarity).
Evolutionary Conservation
Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf.
Publication Abstract from PubMed
Bleomycins constitute a widely studied class of complex DNA cleaving natural products that are used to treat various cancers. Since their first isolation, the bleomycins have provided a paradigm for the development and discovery of additional DNA-cleaving chemotherapeutic agents. The bleomycins consist of a disaccharide-modified metal-binding domain connected to a bithiazole/C-terminal tail via a methylvalerate-Thr linker and induce DNA damage after oxygen activation through site-selective cleavage of duplex DNA at 5'-GT/C sites. Here, we present crystal structures of two different 5'-GT containing oligonucleotides in both the presence and absence of bound Co(III).bleomycin B(2). Several findings from our studies impact the current view of bleomycin binding to DNA. First, we report that the bithiazole intercalates in two distinct modes and can do so independently of well ordered minor groove binding of the metal binding/disaccharide domains. Second, the Co(III)-coordinating equatorial ligands in our structure include the imidazole, histidine amide, pyrimidine N1, and the secondary amine of the beta aminoalanine, whereas the primary amine acts as an axial ligand. Third, minor groove binding of Co(III).bleomycin involves direct hydrogen bonding interactions of the metal binding domain and disaccharide with the DNA. Finally, modeling of a hydroperoxide ligand coordinated to Co(III) suggests that it is ideally positioned for initiation of C4'-H abstraction.
Crystal structure of DNA-bound Co(III) bleomycin B2: Insights on intercalation and minor groove binding.,Goodwin KD, Lewis MA, Long EC, Georgiadis MM Proc Natl Acad Sci U S A. 2008 Apr 1;105(13):5052-6. Epub 2008 Mar 24. PMID:18362349[1]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
See Also
References
- ↑ Goodwin KD, Lewis MA, Long EC, Georgiadis MM. Crystal structure of DNA-bound Co(III) bleomycin B2: Insights on intercalation and minor groove binding. Proc Natl Acad Sci U S A. 2008 Apr 1;105(13):5052-6. Epub 2008 Mar 24. PMID:18362349
