Purification and part characterization of a novel antibacterial protein Scygonadin, isolated from the seminal plasma of mud crab, Scylla serrata (Forskål, 1775)

A novel protein was isolated from the seminal plasma of the mud crab, Scylla serrata (Forskål, 1775). It exhibited an antibacterial activity against the Gram-positive bacterium Micrococcus leteus with IC90 of 0.125 mg/ml. The extraction procedure for the protein included techniques of acid extraction, ion-exchange chromatography on SP-Sepharose Fast Flow and reverse-phase liquid chromatography on Source 5R RPC. It showed a molecular mass of 10.8 kDa by SDS-PAGE. A partial 20 residue NH2-terminal sequence was determined by Edman degradation and MS-fingerprint of the protein was conducted. Similarity search in protein databases (BLAST) revealed that the protein exhibited no significant homology to any other reported antimicrobial peptides. We propose the name Scygonadin (from the gonad of S. serrata) for this antibacterial protein.