Molecular characterization, recombinant expression and bioactivity profile of an antimicrobial peptide, Ss-arasin from the Indian mud crab, Scylla serrata.

Antimicrobial peptides (AMP) are potential alternatives to conventional antibiotics with the prospect to treat infections caused by multidrug resistant bacteria. This is the report of the first arasin sequence from the mud crab, Scylla serrata, designated as Ss-arasin. The complete cDNA sequences of the open reading frame (ORF) is comprised of 198 bp encoding 65 amino acid with a predicted molecular weight of 7 kDa and a predicted isoelectric point of 10.68. The sequence of the N-terminal 24 amino acid residues is indicative of a signal sequence directing the newly synthesize protein toward the secretory pathway. The 41-residue mature peptide is composed of two domains, an N-terminal Gly/Arg-rich domain and a C-terminal cysteine-rich domain. Challenging the mud crab with lipopolysaccharide (LPS) increased expression of Ss-arasin mRNA in haemocytes, reaching the highest level at 6 h, before dropping to basal levels at 24 h. Recombinant rSs-arasin showed antimicrobial activity against three bacterial species Staphylococcus aureus (40 mM), Pseudomonas aeruginosa (40 mM) and Escherichia coli (40 mM) implying significant anti-bacterial action. In addition, recombinant rSs-arasin inhibited human cervical carcinoma (HeLa) and colon carcinoma (HT-29) cell growth. These initial findings are encouraging to further study the structure-activity relationships to optimize these biological functions for future drug development.