cDNA cloning and antigen-binding sites of the MHC class I in Chinese native chicken (Qingyuan Partridge chicken)

Author: Yin Dai, Fangfang Chen, Xuelan Liu, Xian Wang, Hong Ye and Weiyi Yu ^*

Received 11 August 2009, accepted 22 December 2009.

Abstract

Although the number of studies focusing on the major histocompatibility complex I (MHC class I) in poultry is increasing, the MHC class I is still poorly understood in diseases detailedly. In order to further investigate the relationship between the MHC class I and resistance to diseases, we cloned thirty MHC class I of Qingyuan Partridge chickens by RT-PCR and analyzed the amino acid sequences. These MHC class I genes encoded 344 or 355 amino acids. A total of 16 amino acid residues showed polymorphism by Wu-kabat index analysis in the peptide-binding domains (PBDs). The variability with high scores (≥8) was found at four amino acid sites (9, 111, 113 and 153) corresponding to those that can interact with antigenic peptides from the protein model. Our results revealed that the PBD of the Qingyuan Partridge chicken MHC class I is highly polymorphic. Different MHC class I haplotypes associated with different disease resistances in chickens have been confirmed. We compared our MHC class I sequences with six chicken MHC class I from disease-related haplotypes, some high variant sites (score≥8) studied in Qingyuan Partridge chickens were different between resistant and susceptible sequences. In addition, according to the eight conserved HLA-A amino acids that bind with antigen polypeptides, we found that six amino acid residues (Y7, G26, Y58, Y84, Y156 and Y168) in the PBDs were invariable in all our sequences. The phylogenetic trees showed that the PBDs of MHC class I contained 21 different α1 domains and 18 different α2 domains, and some sequences had the same direction of evolution with the resistance-related sequences. As mentioned above, we concluded that the characteristics of PBD in MHC class I were closely linked to diseases.

Key words: Qingyuan Partridge chicken, MHC class I, peptide-binding domain, disease resistance.