title: Characterization of an i-type lysozyme gene from the sea cucumber Stichopus japonicus, and enzymatic and nonenzymatic antimicrobial activities of its recombinant protein.
abstract: Because sea cucumbers lack a well-developed immune system and can ingest pathogenic bacteria together with food, some form of active antibacterial substances must be present in the body for defense. In this study, the cDNA of an i-type lysozyme from the sea cucumber Stichopus japonicus (designated SjLys) was cloned by RT-PCR and RACE PCR techniques. The full length cDNA of SjLys was 713 bp with an open reading frame of 438 bp coding for 145 amino acids. Two catalytic residues (Glu34 and Asp47), conserved in i-type lysozymes, and a highly conserved region near the active site, MDVGSLSCG(P\Y)(Y\F)QIK, were detected in SjLys. In addition, the domain structure analysis of SjLys showed that it is highly similar to the medicinal leech destabilase, which belongs to a new phylogenetic family of invertebrate lysozymes possessing both glycosidase and isopeptidase activities. To gain insight into the in vitro antimicrobial activities of SjLys, the mature peptide coding region was heterologously expressed in Escherichia coli. The recombinant SjLys protein displayed an inhibitive effect on the growth of the tested Gram-positive and Gram-negative bacteria. A remarkable finding is that the recombinant SjLys exhibited more potent activities against all tested bacterial strains after heat-treating at 100 degrees C for 50 min. These results indicated that the S. japonicus lysozyme is an enzyme with combined enzymatic (glycosidase) and nonenzymatic antibacterial action.
authors.affiliation: Department of Biotechnology, School of Biological and Food Engineering, Dalian Polytechnic University, Dalian 116034, China.
authors.forename: Lina
authors.initials: L
authors.lastname: Cong
authors.forename: Xijian
authors.initials: X
authors.lastname: Yang
authors.forename: Xiuxia
authors.initials: X
authors.lastname: Wang
authors.forename: Mikiro
authors.initials: M
authors.lastname: Tada
authors.forename: Meiling
authors.initials: M
authors.lastname: Lu
authors.forename: Heng
authors.initials: H
authors.lastname: Liu
authors.forename: Beiwei
authors.initials: B
authors.lastname: Zhu
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology; D001483:Base Sequence; D004926:Escherichia coli / Q000378:metabolism; D048168:Escherichia coli K12 / Q000187:drug effects / Q000254:growth & development; D006026:Glycoside Hydrolases / Q000378:metabolism* / Q000494:pharmacology; D008969:Molecular Sequence Data; D009113:Muramidase / Q000378:metabolism* / Q000494:pharmacology; D011994:Recombinant Proteins / Q000378:metabolism / Q000494:pharmacology; D012616:Sea Cucumbers / Q000201:enzymology*
chemical_list: D000900:Anti-Bacterial Agents; D011994:Recombinant Proteins; D006026:Glycoside Hydrolases; D009113:Muramidase