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XB-ART-56526
J Immunol 2020 Jan 01;2041:147-158. doi: 10.4049/jimmunol.1900865.
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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 .


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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 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 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.

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Species referenced: Xenopus laevis
Genes referenced: mhc1-uaa myh4 myh6

References [+] :
Adams, PHENIX: building new software for automated crystallographic structure determination. 2002, Pubmed