Peptide binding specificities of HLA-B＊5701 and B＊5801

Recently, genome wide association studies showed that there is a strong association between abacavir-induced serious, idio- syncratic, adverse drag reactions （ADRs） and human leukocyte antigen-B＊5701 （HLA-B＊5701）. Studies also found that ab- acavir-induced ADRs were seldom observed in patients carrying the HLA-B＊5801 subtype. HLA-B＊5801 of the same sero- type （B17） as B＊5701 differs by only 4 amino acids from B＇5701. It is believed that because of these sequence differences, HLA-B＊5801 cannot bind the specific peptides which are required for HLA-B＊5701 to stimulate the T cell immune response. Thus, the difference in peptide binding profiles between HLA-B＊5701 and B＊5801 is an important clue for exploring the mechanisms of abacavir-induced ADRs. VHSE （principal component score vector of hydrophobic, steric, and electronic prop- erties）, a set of amino acid structural descriptors, was employed to establish QSAR models of peptide-binding affinities of HLA-B＊5701 and B＊5801. Optimal linear SVM （support vector machine） models with high predictive capabilities were ob- tained for both B＊5701 and B＇5801. The R2 （coefficient of determination）, Q2 （cross-validated R：）, and RpRE2 （R2 of test set） of two optimal models were 0,7530, 0.7037, 0.6153 （B＇5701） and 0.6074, 0.5966, 0.5762 （B＊5801）, respectively. For B＇5701 and B＇5801, the mutations in positions 45 （MET-THR） and 46 （ALA-GLU） have little influence on the selection specificity of the P2 position of the bound peptide. However, the mutation in position 97 （VAL-ARG） greatly influences the selection speci- ficity of the P7 position. HLA-B＊5701 prefers the bulky and positively charged amino acids at the P7 position. In contrast, HLA-B＊5801 prefers the non-polar hydrophobic amino acids at the P7 position while positively charged amino acids are un- favored.