Abstract
article i nfo Background: The sea cucumber lysozyme belongs to the family of invertebrate lysozymes and is thought to be a key defense factor in protecting aquaculture animals against bacterial infection. Recently, evidence was found that the sea cucumber lysozyme exerts broad spectrum antimicrobial action in vitro against Gram-negative and Gram-positive bacteria, and it also has more potent antimicrobial activity independent of its enzymatic activity. To explore the antimicrobial role of this non-enzymatic lysozyme and model its structure to novel antimicrobial peptides, the peptide from the C-terminal amino acid residues 70-146 of the sea cucumber lysozyme in Stichopus japonicus (SjLys-C) was heterologously expressed in Escherichia coli Rosetta(DE3)pLysS. Results: The fusion protein system led to over-expression of the soluble and highly stable product, an approximate 26 kDa recombinant SjLys-C protein (rSjLys-C). The present study showed that rSjLys-C displayed strong antimicrobial activity against the tested Gram-positive and Gram-negative bacteria. In particular, the heat-treated rSjLys-C exhibited more inhibitive activity than the native rSjLys-C. The structural analysis of SjLys-C showed that it is a typical hydrophilic peptide and contains a helix-loop-helix motif. The modeling of SjLys-C molecular structures at different temperatures revealed that the tertiary structure of SjLys-C at 100°C underwent a conformational change which is favorable for enhancing antimicrobial activity. Conclusion: These results indicate that the expressed rSjLys-C is a highly soluble product and has a strong antimicrobial activity. Therefore, gaining a large quantity of biologically active rSjLys-C will be used for further biochemical and structural studies and provide a potential use in aquaculture and medicine.
Highlights
Among the antimicrobial peptides, lysozyme, having strong bactericidal capability, is considered as the major component of the innate immune system of many organisms and plays an important role in protecting the host species from microbial invasion [1,2]
Further analysis showed that the native rSjLys-C displayed a remarkable inhibitory effect on the growth of M. lysodeikticus, V. parahaemolyticus and V. splendidus, and to a lesser extent on the growth of S. aureus, B. cereus, P. aeruginosa, P. nigrifaciens and A. hydrophila
The antimicrobial activity of the heat-treated rSjLys-C was increased by 21.1% against M. lysodeikticus, 19.0% against V. parahaemolyticus and 11.4% against V. splendidus as compared to the antimicrobial spectrum of the native rSjLys-C
Summary
Lysozyme, having strong bactericidal capability, is considered as the major component of the innate immune system of many organisms and plays an important role in protecting the host species from microbial invasion [1,2]. Lysozyme can kill Gram-negative bacteria and inactivate viruses through a mechanism independent of its muramidase activity [7,8,9,10,11,12]. Evidence was found that the sea cucumber lysozyme exerts broad spectrum antimicrobial action in vitro against Gram-negative and Gram-positive bacteria, and it has more potent antimicrobial activity independent of its enzymatic activity. To explore the antimicrobial role of this non-enzymatic lysozyme and model its structure to novel antimicrobial peptides, the peptide from the C-terminal amino acid residues 70–146 of the sea cucumber lysozyme in Stichopus japonicus (SjLys-C) was heterologously expressed in Escherichia coli Rosetta(DE3)pLysS. The present study showed that rSjLys-C displayed strong antimicrobial activity against the tested Gram-positive and Gram-negative bacteria. Conclusion: These results indicate that the expressed rSjLys-C is a highly soluble product and has a strong antimicrobial activity. Gaining a large quantity of biologically active rSjLys-C will be used for further biochemical and structural studies and provide a potential use in aquaculture and medicine
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