Pocket Mutations of HLA-B27 Show That Anchor Residues Act Cumulatively to Stabilize Peptide Binding

Abstract

Major histocompatibility complex (MHC) class I molecules bind endogenously synthesized peptides for presentation to cytotoxic T-cells. The human class I molecule HLA-B27 consists of a trimolecular complex containing the HLA-B27 heavy chain, a peptide that is usually nine amino acid residues (aa) long, and beta 2-microglobulin (beta 2m). The key interactions for peptide selectivity are between Glu-45, which forms a salt bridge with the Arg at P2 of the peptide, and Asp-116 which favors the binding of peptides containing a Lys or Arg at P9. The t1/2 of dissociation of [125I]beta 2m was measured for peptide-specific HLA-B27 wild-type (wt) and mutant complexes. HLA-B27 wt and HLA-B27 D116F formed relatively stable complexes, with a t1/2 of dissociation on the scale of hours, with appropriate peptides that contained Arg at P2, whereas HLA-B27 E45T required a Gln at P2. Similarly, kinetically stable D116F complexes were formed only with peptides that contained a Leu or Val at P9 instead of Arg or Lys. The [125I]beta 2m dissociation rate data were fit to a set of equations in order to calculate relative binding coefficients for each anchor residue at P2 and P9. The P2 coefficients were sensitive to the E45T mutation but not the D116F mutation, whereas the P9 coefficients were sensitive only to the D116F mutation. Thus, drastic structural changes in one subsite do not affect the other subsite, indicating that the dominant anchor residues at P2 and P9 independently contribute to stabilizing the class I/peptide complex.

Rational design of nonnatural peptides as high-affinity ligands for the HLA-B*2705 human leukocyte antigen.

“…5). This result, in agreement with recent binding data (46), demonstrates that auxiliary anchors at P5 and P7 are not absolutely needed for binding to the HLA-B27 molecule. More importantly, peptides with organic fragments such as Aba3 or Aha2 between P3 and P9 have not lost affinity for HLA-B27 (Fig.…”

Peptides eluted from HLA-B27 of human splenocytes and blood cells reveal a similar but partially different profile compared to in vitro grown cell lines

“…Actually, profiles Arg (P2)-Lys (P9), Arg (P2)-Arg (P9) and Arg (P2)-Phe (P9), "acceptable" for all B27 subtypes with the exception of B * 2709 [10,24], were present in 11 peptides. However, only little interaction between P2 and P9 for B27 peptide-binding stability was reported [25]. Incomplete peptide sequences ( Table 2) confirm preference for residues of Arg, Phe and Leu at P9.…”

Physical and functional independency of p70 and p58 natural killer (NK) cell receptors for HLA class I: their role in the definition of different groups of alloreactive NK cell clones.

“…To define the reactivity of the Z27 mAb with B2705-specific clones (18) (24)(25)(26)(27), and both mutants were also shown to affect recognition by B2705-specific NK clones (23). The corresponding ClR transfectants were used as target cells, and clones FG22, FG50, FG55, and SA260 (all characterized by the p58-/p70+ surface phenotype) were used as effectors.…”