Proteins of the major histocompatibility complex (for humans, human leukocyte antigens, HLA) are involved in the presentation of antigenic peptides for recognition by T-cell receptors, playing an important role in the regulation of the adaptive immune response. HLA class I proteins (encoded by the HLA-A, HLA-B, HLA-C genes) bind peptides 8-13 amino acids in the groove. HLA genes have an exceptionally high degree of variability - several thousand allelic variants are known for each. MHC polymorphisms affect both the binding peptide repertoire and interaction with TCR. The aim of this work is to study the variability of immunologically significant HLA regions which contact TCR and peptide. The most common HLA alleles, cumulatively covering 95% of the human population, were selected for analysis. Amino acid sequences were retrieved from the IPD-IMGT/HLA Database [1]. The HLA positions most likely to contact the peptide and TCR were determined by the calculation of contact frequencies in the TCR-peptide-MHC crystal structures from the Protein Data Bank (PDB) [2]. The heterogeneity of the HLA amino acid sequence was also investigated for individual groups of alleles. Position variability in multiple alignment was assessed and compared with the frequency of amino acid contacts in these positions.
