Crystallization of SLA-2*04:02:02 complexed with a CTL epitope derived from FMDV.

Presentation of viral epitopes by swine MHC I (termed leukocyte antigen class I, SLA I) to cytotoxic T lymphocytes (CTLs) is crucial for swine immunity. The SLA-2 structure, however, remains largely unknown. To illustrate the structural basis of swine CTL epitope presentation, the crystal structure of SLA-2*04:02:02 complexed with one peptide, derived from foot-and-mouth disease virus (FMDV), was analyzed in this study. SLA-2*04:02:02 and swine β2-microglobulin (sβ2m) were refolded in vitro in the presence of peptides. X-ray diffraction data of SLA-2*04:02:02-peptide-sβ2m (referred to as p/SLA-2*04:02:02) were collected. The diffraction dataset was 2.3 Å in resolution and the space group was P3(2)21. Relevant data included a = 101.8 Å, b = 101.8 Å, c = 73.455 Å,α = 90.00°, β = 90.00°, γ = 120.00°. The structure of p/SLA-2*04:02:02 was analyzed. The results revealed that Glu24, Met68, Gly76, and Gln173 in PBG of SLA-2*04:02:02 are different from other MHC I. Furthermore, Asn63 is different from other SLA I. Gln57, Met174 and Gln180 in PBG of SLA I are different from other species' MHC I. All of these features are different from known mammalian peptide-MHC class I complexes (referred to as p/MHC I). In addition, P4-His, P6-Val, and P8-Pro in the peptide were exposed, and these residues as epitopes can be presented by SLA-2*04:02:02. This study not only provides a structural basis for peptide presentation by SLA-2, but also screens one potential FMDV CTL epitope. The results may be of interest in future vaccine development.