Abstract
SpHyastatin was first identified as a new cationic antimicrobial peptide in hemocytes of the mud crab Scylla paramamosain. Based on the amino acid sequences deduced, it was predicted that this peptide was composed of two different functional domains, a proline-rich domain (PRD) and a cysteine-rich domain (CRD). The recombinant product of SpHyastatin displayed potent antimicrobial activities against the human pathogen Staphylococcus aureus and the aquatic animal pathogens Aeromonas hydrophila and Pseudomonas fluorescens. Compared with the CRD of SpHyastatin, the PRD presented better antimicrobial and chitin binding activities, but both regions were essential for allowing SpHyastatin complete antimicrobial activity. The binding properties of SpHyastatin to different microbial surface molecules suggested that this might be an initial and crucial step for performing its antimicrobial activities. Evaluated using propidium iodide uptake assays and scanning electron microscopy images, the antimicrobial mechanism of SpHyastatin was found to be prone to disrupt cell membrane integrity. Interestingly, SpHyastatin exerted its role specifically on the surface of S. aureus and Pichia pastoris whereas it directly killed P. fluorescens through simultaneous targeting the membrane and the cytoplasm, indicating that SpHyastatin could use different antimicrobial mechanisms to kill different species of microbes. As expected, the recombinant SpHyastatin increased the survival rate of crabs challenged with Vibrio parahaemolyticus. In addition, SpHyastatin could modulate some V. parahaemolyticus-responsive genes in S. paramamosain.
Highlights
Antimicrobial peptides are widespread in microbes, plants and animals and they serve as a first line of defense against pathogen invasion (Lay and Anderson, 2005; Hancock and Sahl, 2006; Goyal et al, 2013; Sun et al, 2014; Wang et al, 2015)
proline-rich domain (PRD) and cysteine-rich domain (CRD) and shared a certain similarity with H. araneus hyastatin (Sperstad et al, 2009) and some shrimp penaeidins (O’Leary and Gross, 2006; Woramongkolchai et al, 2011). These studies revealed that the domain of either PRD or CRD is generally contributed to the antimicrobial activity of an antimicrobial peptide (AMP), even with the similar domains of PRD and CRD the antimicrobial activity are different among AMPs
The finding of SpHyastatin with multi-domain structure attracted our attention to further explore what antimicrobial feature of SpHyastatin may have and is it unique or similar to that confirmed in other AMPs? The structure-activity studies demonstrated that PRD SpHyastatin alone showed potent antimicrobial activity with minimum inhibitory concentration (MIC) values a little higher than SpHyastatin mature peptide, while CRD SpHyastatin displayed a relative weak antimicrobial activity
Summary
Antimicrobial peptides are widespread in microbes, plants and animals and they serve as a first line of defense against pathogen invasion (Lay and Anderson, 2005; Hancock and Sahl, 2006; Goyal et al, 2013; Sun et al, 2014; Wang et al, 2015). Several forms of antimicrobial mechanisms of AMPs are known, it is generally accepted that most AMPs are prone to inhibit or kill varieties of pathogens by directly altering or disrupting their cell membranes. AMPs possess multi-functionality except for their direct antimicrobial activities (Lai and Gallo, 2009; Smith and Dyrynda, 2015). They can modulate host gene expression, function in chemotaxis, induce/inhibit cytokine production, etc. The multiple immunomodulatory reactions of AMPs are thought of as potential enhancement of host defense against invading infectious agents
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