Purification and characterization of antibacterial proteins from granular hemocytes of Indian mud crab, Scylla serrata

Marine invertebrates depend upon antimicrobial peptides (AMPs) as a major component of innate immunity, as they are rapidly synthesized and diffuse upon pathogen invasion. In this study, we report the identification and characterization of a 11 kDa antimicrobial protein, which we name SSAP (for Scylla serrata antimicrobial protein), from granular hemocytes of the mangrove crab S. serrata. The protein is highly similar to scygonadin, a male-specific AMP isolated from the ejaculatory duct of S. serrata. SSAP was isolated using various chromatographic techniques, viz. ion-exchange, ultra filtration and RP-HPLC, and demonstrated antibacterial activity against Gram positive and Gram negative bacteria. Full length mRNA encoding SSAP was amplified using a combination of RT-PCR and RACE. The nucleotide sequence revealed a full-length ORF of 381 bp coding for a preprotein of 126 amino acids comprising a signal peptide of 24 amino acids and a mature protein of 102 amino acids with a predicted mass of 11435 Da and pI of 5.70. Unlike scygonadin, SSAP is expressed in several tissues of both male and female crabs, as evidenced by RT-PCR, Northern and Western blot analyses. The study suggests that SSAP might be an isoform or a variant of scygonadin and might play an important role in regulating the immunity of the crab upon microbial infection

Augmentation of Cationic Antimicrobial Peptide Production with Histone Deacetylase Inhibitors as a Novel Epigenetic Therapy for Bacterial Infections

The emergence of antibiotic resistance seriously threatens our ability to treat many common and medically important bacterial infections. Novel therapeutics are needed that can be used alone or in conjunction with antibiotics. Cationic antimicrobial peptides (CAMPs) are important effectors of the host innate defense that exhibit broad-spectrum activity against a wide range of microorganisms. CAMPs are carried within phagocytic granules and are constitutively or inducibly expressed by multiple cell types, including epithelial cells. The role of histone modification enzymes, specifically the histone deacetylases (HDAC), in down-regulating the transcription of CAMP-encoding genes is increasingly appreciated as is the capacity of HDAC inhibitors (HDACi) to block the action of HDACs to increase CAMP expression. The use of synthetic and natural HDACi molecules to increase CAMPs on mucosal surfaces, therefore, has potential therapeutic applications. Here, we review host and pathogen regulation of CAMP expression through the induction of HDACs and assess the therapeutic potential of natural and synthetic HDACi based on evidence from tissue culture systems, animal models, and clinical trials