6A2B

Crystal Structure of Xenopus laevis MHC I complex

Summary for 6A2B

• Entry DOI: 10.2210/pdb6a2b/pdb
• Descriptor: MHC class I antigen, Beta-2-microglobulin, TYR-MET-MET-PRO-ARG-HIS-TRP-PRO-ILE (3 entities in total)
• Functional Keywords: xenopus laevis, mhc i, evolution, immune system
• Biological source: Xenopus laevis (African clawed frog); More
• Total number of polymer chains: 3
• Total formula weight: 43819.81

Authors

Ma, L.Z.,Xia, C. (deposition date: 2018-06-10, release date: 2019-10-23, Last modification date: 2024-11-20)

Primary citation

Ma, L.,Zhang, N.,Qu, Z.,Liang, R.,Zhang, L.,Zhang, B.,Meng, G.,Dijkstra, J.M.,Li, S.,Xia, M.C.
A Glimpse of the Peptide Profile Presentation byXenopus laevisMHC Class I: Crystal Structure of pXela-UAA Reveals a Distinct Peptide-Binding Groove.
J Immunol., 204:147-158, 2020

PubMed Abstract: The African clawed frog, , is a model species for amphibians. Before metamorphosis, tadpoles do not efficiently express the single classical MHC class I (MHC-I) molecule -UAA, but after metamorphosis, adults express this molecule in abundance. To elucidate the Ag-presenting mechanism of -UAA, in this study, the -UAA structure complex (p-UAAg) bound with a peptide from a synthetic random peptide library was determined. The amino acid homology between the -UAA and MHC-I sequences of different species is <45%, and these differences are fully reflected in the three-dimensional structure of p-UAAg. Because of polymorphisms and interspecific differences in amino acid sequences, p-UAAg forms a distinct peptide-binding groove and presents a unique peptide profile. The most important feature of p-UAAg is the two-amino acid insertion in the α2-helical region, which forms a protrusion of ∼3.8 Å that is involved in TCR docking. Comparison of peptide-MHC-I complex (pMHC-I) structures showed that only four amino acids in β2-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 β2-microglobulin. Additionally, the binding distance between pMHC-I and CD8 molecules in nonmammals is different from that in mammals. These unique features of p-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.

PubMed: 31776204
DOI: 10.4049/jimmunol.1900865

Experimental method

X-RAY DIFFRACTION (2.8 Å)