Abstract In order to clarify the structure of duck major histocompatibility complex (MHC ) class I, duck MHC class I light chain cDNA (Anpl -b2m) was cloned from a duck cDNA library by Full RACE PCR.. Subsequently, the mature protein of 2m gene was expressed solubility in pMAL-p2X /E. coli TB1 system. The expressed MBP-2m fusion proteins were purified, cleaved by the Factor Xa protease and Western-blot analysis. The purified MBP-2m, and MBP were analyzed by circular dichroism (CD) spectrum. The duck MHC class I light chain (Anpl -b2m) is 792bp length, containing 18bp 5'-UT and 414bp 3'-UT; The mature peptides of the Anpl-b2m encoded 119 amino acids, including 20 aa of signal peptide and 99 aa of mature protein. According to the sequences analysis, two cysteines are involved in the Ig-folding of the molecule within the 25 and 80 sites, and the ¨YTCRVDH〃 arround the cysteine at the 80 site is similar to the YxCxVxH Ig-motif character. The Anpl -b2m shares a 30.3%-65.9% aa homology with the chicken, fish, frog, human and mouse. Analysis by circular dichroism (CD) spectrum of purified Anpl-b2m protein revealed that the Anpl-b2m protein displayed typical sheet structure and the contents of 冄-helix,-sheet, turn, and random coil were 0aa, 50 aa, 23aa, 26 aa, respectively. The 3D of Anpl-b2m proteins by homology modeling were similar as the 3 human b2mˇs.
