- Article -
| In Silico Biology 9, 0022 (2009); ©2009, Bioinformation Systems e.V. |
HIV1 V3 loop hypermutability is enhanced by the guanine usage bias in the part of env gene coding for it
Vladislav Victorovich Khrustalev
Department of General Chemistry, Belarussian State Medical University, 83 Dzerzinskogo Prospect, Minsk 220000, Belarus
* Corresponding author
Email: vvkhrustalev@mail.ru
Edited by E. Wingender; received December 11, 2008; revised March 03 and May 05, 2009; accepted May 21, 2009; published August 02, 2009
Abstract
Guanine is the most mutable nucleotide in HIV genes because of frequently occurring G to A transitions, which are caused by cytosine deamination in viral DNA minus strands catalyzed by APOBEC enzymes. Distribution of guanine between three codon positions should influence the probability for G to A mutation to be nonsynonymous (to occur in first or second codon position). We discovered that nucleotide sequences of env genes coding for third variable regions (V3 loops) of gp120 from HIV1 and HIV2 have different kinds of guanine usage biases. In the HIV1 reference strain and 100 additionally analyzed HIV1 strains the guanine usage bias in V3 loop coding regions (2G>1G>>3G) should lead to elevated nonsynonymous G to A transitions occurrence rates. In the HIV2 reference strain and 100 other HIV2 strains guanine usage bias in V3 loop coding regions (3G>2G>1G) should protect V3 loops from hypermutability. According to the HIV1 and HIV2 V3 alignment, insertion of the sequence enriched with 2G (21 codons in length) occurred during the evolution of HIV1 predecessor, while insertion of the different sequence enriched with 3G (19 codons in length) occurred during the evolution of HIV2 predecessor. The higher is the level of 3G in the V3 coding region, the lower should be the immune escaping mutation occurrence rates. This hypothesis was tested in this study by comparing the guanine usage in V3 loop coding regions from HIV1 fast and slow progressors. All calculations have been performed by our algorithms "VVK In length", "VVK Dinucleotides" and "VVK Consensus" (www.barkovsky.hotmail.ru).
Keywords: HIV1, HIV2, APOBEC, mutational pressure, gp120; V3 loop, guanine usage, fast AIDS progressors, slow AIDS progressors, codon usage bias, immune escaping