Prospecção de mutações presentes nas proteínas do envelope do vírus chikungunya circulante em Alagoas e seu potencial impacto no reconhecimento de linfócitos B e T citotóxicos

Abstract

Chikungunya virus (CHIKV) is an emergent arbovirus, transmitted by Aedes spp. mosquitoes, that causes a disease characterized by fever, headache, rash, myalgia, and severe persistent polyarthralgia. The CHIKV genome is a positive-sense singlestranded RNA, making it susceptible to mutations during its replication on host cells, which confers adaptive advantages, such as immune system escape. The aim of this study was prospect mutations in the CHIKV genome regions coding for the envelope proteins, occurred at an outbreak in 2016 in the state of Alagoas, seeking to understand their potential impact on the antigenic profile of proteins, through computational analysis. In this way, the viral genome regions for E1, E2, E3, and 6K proteins were sequenced using thirteen patient’s samples diagnosed with CHIKV by RT-qPCR in SUS/Alagoas. The sequences were evaluated by in silico analysis and immunoinformatic tools. The results revealed that CHIKV circulating in Alagoas belongs to the ECSA genotype. Also, it was identified fourteen amino acid substitutions, three of them in E1 glycoprotein, one in 6K protein, nine in E2 glycoprotein, and one in E3 glycoprotein. Among them is the E2-G60D mutation, previously described as capable of improving the vector competence of Aedes aegypti. Homology modeling revealed that five mutations occurred in exposed regions of the proteins. All the epitopes present in the structural proteins of CHIKV available in the Immune Epitope Database (IEDB) were screened. Nine mutations belong to regions of 16 experimentally validated epitopes, which 8 of them were linear epitopes and 8 discontinuous epitopes. Of these, the E2-G60D and E2-M74T mutations are part of more than one discontinuous epitope and 6K-I54V was detected in more than one linear epitope. According to the immunoinformatics approach (Kolaskar and Tongaonkar scale, Chou and Fasman scale, Emini scale, Karplus and Schulz scale, Parker scale, BepiPred 2.0 and DiscoTope 2.0), thirteen mutations have the potential to belong to B cell epitopes. Six mutations have caused differences in predictions of linear B-cell epitopes, according to different propensity scales and computational algorithms. Regarding the prediction of peptide processing and presentation by MHC class I (MHC-I), five mutations affected the number of cleavages by the 26S proteasome and immunoproteasome, cleaving at new sites and abolishing other ones. The prediction of affinity for the transporter associated with antigen processing (TAP) was disturbed by mutations positioned in the C-terminal, N-terminal and P2 position of the peptides. The mutations affected the binding affinity of some peptides to some MHC-I alleles, among the twenty-seven most frequent alleles in the world population. These results provide information that can help to understand the impact of CHIKV genetic variability on the immune response and provide important data for the development of immunodiagnostic tests, antibody therapies, and for the design of epitope-based vaccines.