Molano A, Erdjument-Bromage H, Fremont D H, Messaoudi I, Tempst P, Nikolić-Zugić J
Sloan-Kettering Division, Cornell University Graduate School of Medical Sciences, New York, NY 10021, USA.
J Immunol. 1998 Mar 15;160(6):2815-23.
The peptide-binding site of the murine MHC class I molecule H-2Kb contains a deep C pocket, that is critical for peptide binding, as it accepts the anchor phenylalanine or tyrosine residue located in the middle (position 5, P5F/Y) of H-2Kb binding peptides. H-2Kb predominantly binds octameric peptides. By both criteria, H-2Kb is unique among the known murine and human class I molecules, none of which have a deep C pocket or preferentially select octamers. We investigated the relative importance of the C pocket in peptide selection and binding by the MHC. An MHC class I H-2Kb variant, Kbw9, predicted to contain no C pocket, was engineered by replacing valine at MHC9 with tryptophan. This mutation drastically altered the selection of peptides bound to Kbw9. The Kbw9 molecule predominantly, if not exclusively, bound nonamers. New peptide anchor residues substituted for the loss of the P5F/Y:C pocket interaction. P3P/Y, which plays an auxiliary role in binding to Kb, assumed the role of a primary anchor, and P5R was selected as a new primary anchor, most likely contacting the E pocket. These experiments demonstrate that the presence of a deep C pocket is responsible for the selection of octameric peptides as the preferred ligands for Kb and provide insight into the adaptation of peptides to a rearranged MHC groove.
小鼠主要组织相容性复合体I类分子H-2Kb的肽结合位点包含一个深C口袋，这对于肽结合至关重要，因为它接纳位于H-2Kb结合肽中间（第5位，P5F/Y）的锚定苯丙氨酸或酪氨酸残基。H-2Kb主要结合八聚体肽。根据这两个标准，H-2Kb在已知的小鼠和人类I类分子中是独特的，这些分子均没有深C口袋或优先选择八聚体。我们研究了C口袋在MHC肽选择和结合中的相对重要性。通过将MHC9处的缬氨酸替换为色氨酸，构建了一种预测不包含C口袋的I类MHC H-2Kb变体Kbw9。这种突变极大地改变了与Kbw9结合的肽的选择。Kbw9分子主要（如果不是唯一地）结合九聚体。新的肽锚定残基替代了P5F/Y:C口袋相互作用的缺失。在与Kb结合中起辅助作用的P3P/Y承担了主要锚定的作用，并且P5R被选为新的主要锚定，最有可能与E口袋接触。这些实验表明，深C口袋的存在负责选择八聚体肽作为Kb的首选配体，并为肽适应重排的MHC凹槽提供了见解。
