RESUMO
Cholera is a global disease that has persisted for millennia. The cholera toxin (CT) from Vibrio cholerae is responsible for the clinical symptoms of cholera. This toxin is a hetero-hexamer (AB(5)) complex consisting of a subunit A (CTA) with a pentamer (B(5)) of subunit B (CTB). The importance of the AB(5) complex for pathogenesis is established for the wild type O1 serogroup using known structural and functional data. However, its role is not yet documented in other known serogroups harboring sequence level residue mutations. The sequences for the toxin from different serogroups are available in GenBank (release 177). Sequence analysis reveals mutations at several sequence positions in the toxin across serogroups. Therefore, it is of interest to locate the position of these mutations in the AB(5) structure to infer complex assembly for its functional role in different serogroups. We show that mutations in the CTA are at the solvent exposed regions of the AB(5) complex, whereas those in the CTB are at the CTB/CTB interface of the homo-pentamer complex. Thus, the role of mutations at the CTB/CTB interface for B(5) complex assembly is implied. It is observed that these mutations are often non-synonymous (e.g. polar to non-polar or vice versa). The formation of the AB(5) complex involves inter-subunit residue-residue interactions at the protein-protein interfaces. Hence, these mutations, at the structurally relevant positions, are of importance for the understanding of pathogenesis by several serogroups. This is also of significance in the improvement of recombinant CT protein complex analogs for vaccine design and their use against multiple serogroups.
RESUMO
UNLABELLED: The human immunodeficiency virus type-1 (HIV-1) gp160 (gp120-gp41 complex) trimer envelope (ENV) protein is a potential vaccine candidate for HIV/AIDS. HIV-1 vaccine development has been problematic and charge polarity as well as sequence variation across clades may relate to the difficulties. Further obstacles are caused by sequence variation between blood and brain-derived sequences, since the brain is a separate compartment for HIV-1 infection. We utilize a threedimensional residue measure of solvent exposure, accessible surface area (ASA), which shows that major segments of gp120 and gp41 known structures are solvent exposed across clades. We demonstrate a large percent sequence polarity for solvent exposed residues in gp120 and gp41. The range of sequence polarity varies across clades, blood, and brain from different geographical locations. Regression analysis shows that blood and brain gp120 and gp41 percent sequence polarity range correlate with mean Shannon entropy. These results point to the use of protein modifications to enhance HIV-1 ENV vaccines across multiple clades, blood, and brain. It should be noted that we do not address the issue of protein glycosylation here; however, this is an important issue for vaccine design and development. ABBREVIATIONS: HIV-1 - human immunodeficiency virus type 1, AIDS - acquired immunodeficiency syndrome, ENV - envelope, gp160 - 160,000d glycoprotein, gp120 - 120,000d glycoprotein, gp41 - 41,000d glycoprotein, LANL - Los Alamos National Laboratories, PDB - Protein Data Bank, HVTN - STEP HIV vaccine trial, AA - amino acids, MSA - multiple sequence alignment, ASA - accessible surface area, SNPs- single nucleotide polymorphisms, HAART - Highly Active Antiretroviral Therapy, CCR5 - C-C chemokine receptor type 5, CNS - central nervous system, HIVE - HIV encephalitis, P - polarity, NP - non-polarity, CTL - cytotoxic T lymphocyte, NIAID - National Institute of Allergy and Infectious Diseases.