Peptide interactions with the K^b antigen recognition site

The ability of OVA-specific H-2K^b-restricted CTL to recognize the defined OVA_258-276 peptide in the context of the K^bm mutants and variants of these mutants was examined to determine how specific variations in the Ag recognition site-influenced peptide presentation to these CTL. L cells expressing K^b or K^bm10 were equally capable of presenting the OVA peptide to K^b-restricted, OVA-specific bulk CTL, whereas L cell clones expressing K^bm8 or K^bm1 showed little to no capacity to present this peptide. L cell transfectants expressing K^bm3 and K^bm23 consistently demonstrated an intermediate to low level of presentation to bulk OVA-specific CTL. Dissection of the K^bm8 mutant revealed that cells expressing K^bm8-22 (Tyr→Phe) and/or K^bm8-24 (Glu→Ser) presented the OVA peptide significantly less well than the K^b-representing molecule. Presentation of OVA by cells expressing K^bm8-23,30 (Met→Ile) (Asp→Asn), K^bm8-23 (Met→Ile), and K^bm8-30 (Asp→Asn) was equivalent to K^b presentation. Another mutation designated as K^bm5, that has a substitution at position 116 (Tyr→Phe), demonstrated an intermediate to high ability to present OVA_258-276 to an OVA-specific CTL line. The K^bm3, K^bm11, and K^bm23 mutants were unable to present the OVA peptide to this same CTL line. Dissection of these mutants showed that the substitution at position 77 (Asp→Ser), which is shared by all three mutants, was responsible for their inability to present the peptide. A second K^b-restricted CTL line was able to recognize OVA in the context of the Asp→Ser substitution at position 77. The results of this analysis suggest that the OVA_258-276 peptide interacts with multiple regions within the Ag recognition site of the K^b class I protein.