SpStrongylocin 1

A novel crustin-like antimicrobial peptide (Crus-likePm) was identified from haemocytes of Penaeus monodon. The deduced amino acid sequence of a Crus-likePm consists of 124 amino acid residues of the mature peptide and a signal peptide of 17 amino acid residues. The mature peptide contains a glycine-rich domain at the N-terminus and 12 conserved cysteine residues containing a single WAP domain at the C-terminus. Phylogenetic tree and sequence comparison clearly confirmed a distinct between a Crus-likePm and other shrimp crustins. Genomic organization and upstream region of a Crus-likePm gene was investigated. The gene consisted of two exons and one intron. The 5'-flanking regions of a Crus-likePm gene contain multiple putative transcription factor binding sites. mRNA transcript of a Crus-likePm was found to be abundantly expressed in haemocyte and highly up-regulated after Vibrio harveyi injection. The mature Crus-likePm was cloned into the pET28b with an N-terminal hexa-histidine tag fused in-frame, and expressed in E. coli. The purified recombinant Crus-likePm showed strong antimicrobial activity against both Gram-positive and Gram-negative bacteria including V. harveyi, a major pathogenic bacteria in shrimp aquaculture.

Penaeidins, members of a new family of antimicrobial peptides constitutively produced and stored in the haemocytes of penaeid shrimp, display antimicrobial activity against bacteria, and fungi. Here, a DNA sequence encoding the mature Ch-penaeidin peptide was cloned into the pPIC9K vector and transformed into Pichia pastoris. The transformed cells were screened for multi-copy plasmids using increasing concentrations of G418. Positive colonies carrying chromosomal integrations of the Chp gene were identified by phenotype and PCR. When transformed cells were induced with methanol, SDS-PAGE and Western blotting revealed the production of a approximately 6100 Da recombinant CHP (rCHP) expression product. Large scale expression revealed that rCHP was produced at 108 mg/L under optimal conditions in the highest Chp-producing P. pastoris clone. The antimicrobial activities of rCHP were studied by liquid phase analysis, which revealed that rCHP exhibited activities against some Gram-negative and Gram-positive bacteria, but had a relatively low activity against some fungi. Purification of rCHP by cation exchange chromatography and subsequent automated amino acid sequencing revealed the presence of four additional amino acids (YVEF) at the N-terminus that belonged to the cleaved fusion signal peptide; these residues may account for the observed decrease in antifungal activity. Together, these observations indicate that rCHP is an effective antimicrobial peptide that can be successfully produced at high levels in the yeast, and therefore may be a potential antimicrobial candidate for practical use.

Sea urchins possess an innate immune system and are regarded as a potential source for the discovery of new antimicrobial peptides (AMPs). Here we report the purification and characterization of two novel antibacterial peptides (5.6 and 5.8kDa) from coelomocyte extracts of the green sea urchin, Strongylocentrotus droebachiensis. These are the first reported AMPs isolated from sea urchins. The cDNA encoding the peptides and genomic sequences was isolated and sequenced. The two peptides (named strongylocins 1 and 2) have putative isoforms (1b and 2b), similar to two putative proteins from the purple sea urchin S. purpuratus. The native strongylocins are cationic, defensin-like peptides (cysteine-rich), but show no similarity to other known AMPs concerning the cysteine distribution pattern. Strongylocin 1 consists of 83 amino acids that include a preprosequence of 35 amino acids, whereas strongylocins 2a and 2b are composed of 89 and 90 amino acids, respectively, where 38 amino acids represent a preprosequence. No introns were found in the cloned gene of strongylocin 1b, whereas three introns and four exons were found in strongylocins 1a and 2a/b. The latter gene organization was also found in genes coding for putative strongylocins in S. purpuratus. The molecular mass difference between the native peptide and the deduced strongylocin 2 suggests that the first amino acid is bromotryptophan. The native peptides display potent activities against Gram-negative and Gram-positive bacteria.