APPLICATION OF COMPUTATIONAL ALGORITHMS TO ASSESS THE FUNCTIONALITY OF NON-SYNONYMOUS SUBSTITUTIONS IN MHC DRB GENE OF NIGERIAN GOATS

The Major Histocompatibility Complex (MHC) contains highly variable multi-gene families, which play a key role in the adaptive immune response within vertebrates. Among the Capra MHC class II genes, the expressed DRB locus is highly polymorphic, particularly in exon 2, which encodes the antigen-binding site. Models of variable nonsynonymous/synonymous rate ratios among sites may provide important insights into functional constraints at different amino acid sites and may be used to detect sites under positive selection. Many non-synonymous single nucleotide polymorphisms (nsSNPs) at the DRB locus in goats are suspected to impact protein function. This study, therefore, aimed at comparing the efficiency of six computational approaches to predict the likelihood of a particular non-synonymous (amino acid change) coding SNP to cause a functional impact on the protein. This involved the use of PANTHER, SNAP, SIFT, PolyPhen-2, PROVEAN and nsSNPAnalyzer bioinformatics analytical tools in detecting harmful and beneficial effects at H57G, Y89R, V104D and Y112I substitutions in the peptide binding region of the DRB gene of Nigerian goats. The results from PANTHER analysis revealed that H57G, Y89R and Y112I substitutions (P-deleterious= 0.113, 0.204 and 0.472, respectively) were beneficial; while that of V104D was deleterious (P-deleterious=0.756), an indication that it was non-neutral. As regards the SNAP approach, H57G and Y89R substitutions were returned neutral with expected accuracy of 53 and 69%, respectively while V104D and Y112I substitutions were harmful. H57G and Y89R substitutions were also found harmless in the SIFT analysis. However, only H57G (PROVEAN) and V104D (nsSNPAnalyzer) amino acid substitutions were found to be beneficial. Interestingly, the predicted 3D structures of both native and mutant DRB protein appeared similar as validated by Ramachandran plots. The consensus reached by PANTHER, SNAP, SIFT and PolyPhen-2 approaches on the neutrality especially of H57G (PROVEAN inclusive) and Y89R amino acid substitutions may be used in search of disease resistant genotypes at the DRB locus of Nigerian goats.