LAUSR

ABSTRACT Defensins are a group of host defense peptides that play a central role in host innate immune responses. Here, 26 genes encoding &bgr;‐defensin‐like peptides have been identified for the first time in Pelodiscus sinensis using database mining approach. Phylogenetic study confirmed that &bgr;‐defensins are fast evolving genes with high rates of sequence substitutions. The expression level of several selected genes in different tissues was examined by RT‐PCR. Ps‐BDs mainly adopt &bgr;‐strands and/or &agr;‐helix conformations homology modeled by Rosetta program. Further, Ps‐BD2 was expressed in Pichia pastoris and purified using Ni‐NTA column and RT‐HPLC. As expected, the rPs‐BD2 showed strong antimicrobial activity, but displayed a negligible hemolytic and cytotoxic activity on human erythrocytes and Raw 264.7 murine macrophage cells, respectively. Our results suggested that the Ps‐BD2 was produced efficiently in P. pastoris expression system, which makes the large‐scale use of rPs‐BDs possible in the future clinical practice. HIGHLIGHTSTotal 26 &bgr;‐defensins were identified and characterized from Chinese soft shell turtle (Pelodiscus sinensis) EST library.The importance of Ps‐BDs in turtle's innate immune response could be deduced from the expression profiles.Ps‐BDs are predicted to mainly adopt &bgr;‐strands and/or &agr;‐helix conformations homology modeled by Rosetta.Ps‐BD2 with the best character traits of &bgr;‐defesin was expressed in the eukaryotic expression system.The recombinant Ps‐BD2 showed strong antimicrobial activity, but negligible hemolytic and cytotoxic activities.