Secondary structure and 3D homology modeling of swine leukocyte antigen class 2 (SLA-2) molecules

No information to date is available to elucidate the structure of swine leukocyte antigen class I (SLA-I) molecule which is comprised by a heavy chain of SLA-I non-covalently associated with a light chain, β2-microglobulin (β2m) proteins. Presently, one of SLA-I gene SLA-2 and β2m gene were expressed as soluble maltose binding proteins (MBP-proteins) in a pMAL-p2X/Escherichia coli TB1 system and identified by western blotting with anti-MBP polyclonal antibodies. The expressed proteins MBP-SLA-2 and MBP-β2m were purified on amylose affinity columns followed by DEAE–Sepharose. The purified products were cleaved by Factor Xa, respectively, and the interest of proteins SLA-2 and β2m were purified on amylose affinity columns followed by separation from MBP on DEAE–Sepharose. The secondary structures of SLA-2 and β2m were analyzed by circular dichroism (CD) spectrophotometry. The three-dimensional (3D) structure of their peptide-binding domain (PBD) was modeled-based sequence homology. The content of the α-helix, β-sheet, turn, and random coil in the SLA-2 protein were 76, 95, 36, and 67 aa, respectively. In the 98 aa of β2m, the contents of the α-helix, β-sheet, turn, and random coil were 0, 45, 8, and 45 aa, respectively. The SLA-2 protein displayed a typical α-helix structure while β2m protein displayed a typical β-sheet structure. Homology modeling of the SLA-2 and β2m proteins demonstrated similarities with the structure of human and mouse MHC (major histocompatibility complex) class I proteins.