6a2b

Publication Abstract from PubMed

The African clawed frog, Xenopus laevis, is a model species for amphibians. Before metamorphosis, tadpoles do not efficiently express the single classical MHC class I (MHC-I) molecule Xela-UAA, but after metamorphosis, adults express this molecule in abundance. To elucidate the Ag-presenting mechanism of Xela-UAA, in this study, the Xela-UAA structure complex (pXela-UAAg) bound with a peptide from a synthetic random peptide library was determined. The amino acid homology between the Xela-UAA and MHC-I sequences of different species is <45%, and these differences are fully reflected in the three-dimensional structure of pXela-UAAg. Because of polymorphisms and interspecific differences in amino acid sequences, pXela-UAAg forms a distinct peptide-binding groove and presents a unique peptide profile. The most important feature of pXela-UAAg is the two-amino acid insertion in the alpha2-helical region, which forms a protrusion of approximately 3.8 A that is involved in TCR docking. Comparison of peptide-MHC-I complex (pMHC-I) structures showed that only four amino acids in beta2-microglobulin that were bound to MHC-I are conserved in almost all jawed vertebrates, and the most unique feature in nonmammalian pMHC-I molecules is that the AB loop bound beta2-microglobulin. Additionally, the binding distance between pMHC-I and CD8 molecules in nonmammals is different from that in mammals. These unique features of pXela-UAAg provide enhanced knowledge of T cell immunity and bridge the knowledge gap regarding the coevolutionary progression of the MHC-I complex from aquatic to terrestrial species.

A Glimpse of the Peptide Profile Presentation by Xenopus laevis MHC Class I: Crystal Structure of pXela-UAA Reveals a Distinct Peptide-Binding Groove.,Ma L, Zhang N, Qu Z, Liang R, Zhang L, Zhang B, Meng G, Dijkstra JM, Li S, Xia MC J Immunol. 2019 Nov 27. pii: jimmunol.1900865. doi: 10.4049/jimmunol.1900865. PMID:31776204^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.