Mechanism study on a new antimicrobial peptide Sphistin derived from the N-terminus of crab histone H2A identified in haemolymphs of Scylla paramamosain

Oct 18, 2015Fish & shellfish immunology

How a new crab antimicrobial peptide Sphistin from blood fights microbes

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Abstract

A 38-amino acid peptide named Sphistin derived from the histone H2A of the mud crab Scylla paramamosain exhibits significant antimicrobial activity.

Sphistin demonstrated antimicrobial effects against various pathogens, including Aeromonas hydrophila, Pseudomonas fluorescens, and Pseudomonas stutzeri.
The peptide displayed typical features of antimicrobial peptides, such as an amphiphilic α-helical structure and a net positive charge.
Treatment with Sphistin caused leakage of cell contents and disruption of bacterial surfaces, indicating its mechanism of action.
Sphistin increased the permeability of the cytoplasmic membrane in Escherichia coli.
Confocal microscopy revealed that Sphistin binds to the membranes of certain bacteria but does not enter the cytoplasm.
Synthetic Sphistin showed no cytotoxicity to primary cultured crab haemolymphs and mammalian cells even at a concentration of 100 μg/mL.

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Histone H2A is known to participate in host immune defense through generating special antimicrobial peptides (AMPs), for which it has been an interesting research focus to characterize this kind of peptides in vertebrates and invertebrates. Although thousands of AMPs have been reported in variety of life species, only several AMPs are known in crabs and in particular no H2A-derived AMP has yet been reported. In the present study, a 38-amino acid peptide with antimicrobial activity was determined based on the sequence analysis of a histone H2A identified from the mud crab Scylla paramamosain. The histone H2A derived peptide was an AMP-like molecule and designated as Sphistin. Sphistin showed typical features of AMPs such as amphiphilic α-helical second structrue and positive charge net. The synthetic Sphistin exerted high antimicrobial activity against Gram-positive, Gram-negative bacteria and yeast, among which Aeromonas hydrophila, Pseudomonas fluorescens and Pseudomonas stutzeri are important aquatic pathogens. Leakage of the cell content and disruption of the cell surface were observed in bacterial cells treated with Sphistin using scanning electron microscopy. It was proved that the increasing cytoplasmic membrane permeability of Escherichia coli was caused by Sphistin. Further observation under confocal microscopy showed that Sphistin could combine onto the membrane of Staphylococcus aureus, E. coli MC1061 and Pichia pastoris but not translocate into the cytoplasm. Moreover, the affinity of Sphistin with either LPS or LTA was also testified that there was an interaction between Sphistin and cell membrane. Thus, the antimicrobial mechanism of this peptide likely exerted via adsorption and subsequently permeabilization of the bacterial cell membranes other than penetrating cell membrane. In addition, synthetic Sphistin exhibited no cytotoxicity to primary cultured crab haemolymphs and mammalian cells even at a high concentration of 100 μg/mL for 24 h. This is the first report of a histone-derived Sphistin identified from S. paramamosain with a specific antimicrobial activity and mechanism, which could be a new candidate for future application in aquaculture and veterinary medicine.

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Mechanism study on a new antimicrobial peptide Sphistin derived from the N-terminus of crab histone H2A identified in haemolymphs of Scylla paramamosain

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