Molecular characterization and expression analysis of β2-microglobulin in large yellow croaker Pseudosciaena crocea

beta(2)-Microglobulin (beta(2)m), a protein necessary for proper folding, peptide binding, and surface display of class I antigens plays an important role in immune response. The full-length cDNA containing beta(2)m was cloned from the spleen cDNA library of large yellow croaker Pseudosciaena crocea (Pscr-beta (2) m) by expressed sequence tag (EST) analysis. The Pscr-beta (2) m is 926 nucleotides (nt) long, including an open reading frame (ORF) of 348 nt encoding a polypeptide of 116 amino acids (aa). The deduced Pscr-beta (2) m possessed all characteristic domains of beta(2)m in other species, including a 16-aa leader peptide and a typical immunoglobulin (Ig) and major histocompatibility complex protein (MHC) signature YSCRVTH at residues 81-87. Homology modeling showed that the 3D structure of Pscr-beta (2) m protein is similar to that of human beta(2)m, except for a beta-strand (G) being lost in Pscr-beta (2) m due to amino acid deletion (positions 94-95). Tissue expression profile analysis revealed that the Pscr-beta (2) m was constitutively expressed in all tissues examined, such as kidney, spleen, liver, gills, heart, intestine, brain, and muscle, although at different levels. Upon stimulation with poly(I:C) or inactivated trivalent bacterial vaccine, the expression of Pscr-beta (2) m was significantly up-regulated in intestine, kidney and spleen at 24 h post-induction, and increase of Pscr-beta (2) m transcripts was also observed in liver post-induction with poly(I:C). Real-time PCR further revealed that the expression of Pscr-beta (2) m in intestine, kidney and spleen tissues was differentially regulated by poly(I:C) and bacterial vaccine during 72 h of induction. These results suggested that Pscr-beta (2) m might be involved in both antiviral and antibacterial mechanisms in large yellow croaker.