crystallization communications
β2-Microglobulin (β2m) is an essential subunit of the major histocompatibility complex (MHC) class I molecule that helps to stabilize the structure of peptide–MHC I (pMHC I). It is also one of the typical immunoglobulin superfamily (IgSF) molecules in the adaptive immune system (AIS). Sharks belong to the cartilaginous fish, which are the oldest jawed vertebrate ancestors with an AIS to exist in the world. Thus, the study of cartilaginous fish β2m would help in understanding the evolution of IgSF molecules. In order to demonstrate this, β2m from a cartilaginous fish, nurse shark (Ginglymostoma cirratum), was expressed, refolded, purified and crystallized. Diffraction data were collected to a resolution of 2.3 Å. The crystal belonged to space group P3221, with unit-cell parameters a = b = 88.230, c = 67.146 Å. The crystal structure contained two molecules in the asymmetric unit. The results will provide structural information for study of the evolution of β2m and IgSF in the AIS.