Crystallization and preliminary X-ray diffraction analysis of the two distinct types of zebrafish β2-microglobulin

Abstract

β2-Microglobulin (β2m) noncovalently associates with the heavy chain of major histocompatibility complex class I (MHC I) molecules, which bind foreign antigen peptides to control the cytotoxic T lymphocyte (CTL) immune response. In contrast to mammals, there are distinct types of β2ms derived from two loci in a number of teleost species. In order to clarify the structures of the β2ms, the zebrafish (Danio rerio) β2msDare-β2m-I andDare-β2m-II were expressed inEscherichia coli, purified and crystallized, and diffraction data were collected to 1.6 and 1.9 Å resolution, respectively. Both crystals belonged to space groupP212121. The unit-cell parameters were determined to bea= 38.2,b= 50.4,c= 50.9 Å forDare-β2m-I anda= 38.9,b= 52.7,c= 65.8 Å forDare-β2m-II. Each asymmetric unit was constituted of one molecule, with Matthews coefficients of 2.22 and 3.01 Å3 Da−1and solvent contents of 45 and 59% forDare-β2m-I andDare-β2m-II, respectively. These two β2m structures will provide relevant information for further studies of the structures of the MHC I complex.