[Cloning and antimicrobial activity of pigeon avian beta-defensin 5]

The objective of the study was to clone avian beta-defensin (AvBD) 5 gene from pigeon bone marrow tissues and liver tissues, to express the recombinant AvBD5 protein in E. coli, and to determine its antimicrobial activity. The mRNA of duck AvBD5 was cloned from pigeon bone marrow tissues and liver tissues by RT-PCR. In addition, phylogenetic relationships between amino acid sequence of the pigeon AvBD5, AvBDs from other avian species, and some mammalian beta-defensin-5 were analyzed. The cDNA of pigeon AvBD5 was sub-cloned into pGEX-6p-1 vector to construct recombinant plasmid pGEX-pigeon AvBD5. The recombinant protein was expressed into E. coli and purified. Antimicrobial activity and physical-chemical stability of the recombinant fusion protein were measured in vitro. The complete nucleotide sequence of both cDNAs contained 201 bp nucleotides, encoding a polypeptide of 66 amino acids. Both beta-defensins have six conserved cysteines. Phylogenetic relationships were analyzed. Both pigeon AvBDs shared the highest amino acid homology (87.9% and 78.8%) with duck AvBD5. So it was named as pigeon AvBD5alpha (bone marrow) and AvBD5beta (liver). Both recombinant plasmids were transformed into E. coli BL21 and the bacteria were induced with Isopropyl beta-D-1-Thiogalactopyranoside (IPTG). After purification, antibacterial activity of the purified was investigated. In addition, effect of ionic strength on the antibacterial activity, and hemolytic recombinant protein activity of the purified recombinant protein were investigated. A 32 kDa protein was highly expressed. Both purified recombinant pigeon AvBD5alpha and AvBD5beta exhibited extensive antimicrobial activities against 12 bacteria, including Gram-positive and Gram-negative. In high salt ions concentrations, antibacterial activity of both recombinant proteins was decreased. In addition, the hemolysis activity of recombinant protein was extremely low.