Understanding the obstacle of incompatibility at residue 156 within HLA-B*35 subtypes

Abstract

Defining permissive and non-permissive mismatches for transplantation is a demanding challenge. Single mismatches at amino acid (AA) position 156 of human leucocyte antigen (HLA) class I have been described to alter the peptide motif, repertoire, or mode of peptide loading through differential interaction with the peptide-loading complex. Hence, a single mismatch can tip the balance and trigger an immunological reaction. HLA-B*35 subtypes have been described to evade the loading complex, 156 mismatch distinguishing B*35:01 and B*35:08 changes the binding groove sufficiently to alter the sequence features of the selected peptide repertoire. To understand the functional influences of residue 156 in B*35 variants, we analyzed the peptide binding profiles of HLA-B*35:01156Leu, B*35:08156Arg and B*35:62156Trp. The glycoprotein tapasin represents a target for immune evasions and functions within the multimeric peptide-loading complex to stabilize empty class I molecules and promote acquisition of high-affinity peptides. All three B*35 subtypes showed a tapasin-independent mode of peptide acquisition. HLA-B*35-restricted peptides of low- and high-binding affinities were recovered in the presence and absence of tapasin and subsequently sequenced utilizing mass spectrometry. The peptides derived from B*35 variants differ substantially in their features dependent on their mode of recruitment; all peptides were preferentially anchored by Pro at p2 and Tyr, Phe, Leu, or Lys at pΩ. However, the Trp at residue 156 altered the p2 motif to an Ala and restricted the pΩ to a Trp. Our results highlight the importance of understanding the impact of key micropolymorphism and how a single AA mismatch orchestrates the neighboring AAs.Electronic supplementary materialThe online version of this article (doi:10.1007/s00251-015-0896-4) contains supplementary material, which is available to authorized users.

Polymorphism at residue 156 of the new HLA‐A*02:683 allele suggests immunological relevance

“…The amino acid at position 156 is located in the alpha helix of the HLA‐A molecule, which is part of the peptide binding α2 domain and is replaced by arginine (R), a positively charged, hydrophilic amino acid. Previously, a single amino acid polymorphism at this residue for HLA‐B*44 , HLA‐B*35 and HLA‐A*24 has been reported to alter immune response through changes in peptide loading mode, peptide repertoire and thus, T‐cell recognition . Here, the change in the peptide binding pocket of new HLA molecule has been confirmed by protein modeling (Figure C‐E).…”

“…Previously, a single amino acid polymorphism at this residue for HLA-B*44, HLA-B*35 and HLA-A*24 has been reported to alter immune response through changes in peptide loading mode, peptide repertoire and thus, T-cell recognition. 4 Here, the change in the peptide binding pocket of new HLA molecule has been confirmed by protein modeling (Figure 1C-E). It is clear that the new allele can have a different peptide binding conformation and T-cell recognition compared with the other alleles especially in comparison with HLA-A*02:22:01 ( Figure 1E).…”

Peptide Presentation Is the Key to Immunotherapeutical Success

“…Those HLA subtypes can differ from alleles that are strictly dependent on the association with the PLC for peptide loading only by a single amino acid within the heavy chain, altering the structural interface that interacts with the PLC [10][11][12]. Especially the interaction of TPN, a protein that mediates the binding of high-affinity peptides into the HLA-I PBR, with the HLA-I molecule, is of exquisite importance to produce stable pHLA-I complexes that persist on the cell surface.…”

The polymorphism at residue 156 determines the HLA-B*35 restricted peptide repertoire during HCMV infection

“…Some alleles differ in more than 30 amino acids (AA) from each other, while other differ only by one AA position. However, even a single AA difference that is not predicted to alter the peptide binding motif can result in a complete alteration of the peptide binding repertoire (Badrinath et al 2014 ; Burrows et al 2007 ; Manandhar et al 2016 ). HLA-B*35:01 and HLA-B*35:08 differ only at position 156 with a 156Leu for B*35:01 and a 156Arg for B*35:08; their bound peptides possess different peptide binding characteristics even though AA 156 is not located at the primary peptide binding sites (B and F pocket), but protrudes from the α2-helix into the peptide binding groove (Huyton et al 2012 ).…”

“…The peptide binding motif is generally determined by the AAs in the pockets. Primary anchors for HLA-B*35:01 are Pro at position 2 (p2) and Tyr at the last position (pΩ) (and to a lesser extend Phe, Met, Leu, or Ile) (Falk et al 1993 ; Hill et al 1992 ; Manandhar et al 2016 ; Schönbach et al 1996 ). Additionally, secondary binding preferences are published for Leu, Val, Ile, or Met at p3 (Schönbach et al 1996 ).…”