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.
