Tissue distribution and functional characterization of mytimacin-4 in Mytilus galloprovincialis

Molecular characterization, expression and antibacterial function of a macin, HdMac, from Haliotis discus hannai

Macins are a family of antimicrobial peptides, which play multiple roles in the elimination of invading pathogens. In the present study, a macin was cloned and characterized from Pacific abalone Haliotis discus hannai (Designated as HdMac). Analysis of the conserved domain suggested that HdMac was a new member of the macin family. In non-stimulated abalones, HdMac transcripts were constitutively expressed in all five tested tissues, especially in hemocytes. After Vibrio harveyi stimulation, the expression of HdMac mRNA in hemocytes was significantly up-regulated at 12 hr (P < 0.01). RNAi-mediated knockdown of HdMac transcripts affected the survival rates of abalone against V. harveyi. Moreover, recombinant protein of HdMac (rHdMac) exhibited high antibacterial activities against invading bacteria, especially for Vibrio anguillarum. In addition, rHdMac possessed binding activities towards glucan, lipopolysaccharides (LPS), and peptidoglycan (PGN), but not chitin in vitro. Membrane integrity analysis revealed that rHdMac could increase the membrane permeability of bacteria. Meanwhile, both the phagocytosis and chemotaxis ability of hemocytes could be significantly enhanced by rHdMac. Overall, the results showed that HdMac could function as a versatile molecule involved in immune responses of H. discus hannai.

Marine Antimicrobial Peptides: An Emerging Nightmare to the Life-Threatening Pathogens

The emergence of multidrug-resistant pathogens due to improper usage of conventional antibiotics has created a global health crisis. Alternatives to antibiotics being an urgent need, the scientific community is forced to search for new antimicrobials. This exploration has led to the discovery of antimicrobial peptides, a group of small peptides occurring in different phyla such as Porifera, Cnidaria, Annelida, Arthropoda, Mollusca, Echinodermata, and Chordata, as a component of their innate immune system. The marine environment, possessing immense diversity of organisms, is undoubtedly one of the richest sources of unique potential antimicrobial peptides. The distinctiveness of marine antimicrobial peptides lies in their broad-spectrum activity, mechanism of action, less cytotoxicity, and high stability, which form the benchmark for developing a potential therapeutic. This review aims to (1) synthesise the available information on the distinctive antimicrobial peptides discovered from marine organisms, particularly over the last decade, and (2) discuss the distinctiveness of marine antimicrobial peptides and their prospects.

Identification, antibacterial activities and action mode of two macins from manila clam Venerupis philippinarum

In this study, two macins were identified from clam Venerupis philippinarum (designated as VpMacin-1 and VpMacin-2). They showed 64.71% similarity with each other. The highest mRNA expression of VpMacin-1 and VpMacin-2 was detected in gills and hepatopancreas, respectively, in non-stimulated clams, and their expression could be induced significantly in hemocytes after Vibrio anguillarum infection. Silencing of VpMacin-1 and VpMacin-2 led to 22% and 49% mortality 6 days post infection. Escherichia coli cells were killed by recombinant protein rVpMacin-1 and rVpMacin-2 within 1000 and 400 min, respectively, at a concentration of 1.0 × MIC. Compared with rVpMacin-1, rVpMacin-2 not only showed higher broad-spectrum antimicrobial activities towards Vibrio strains, but possessed stronger abilities to inhibit the formation of bacterial biofilm. Both membrane integrity and electrochemical assay indicated that rVpMacins were capable of causing bacterial membrane permeabilization, especially for rVpMacin-2. Besides, rVpMacin-1 significantly induced both phagocytic (0.1 and 1.0 × MIC, p < 0.05) and chemotactic effects (0.1 × MIC, p < 0.01) of hemocytes, while there was no significant increase for rVpMacin-2. Overall, our results suggested that VpMacin-1 and VpMacin-2 play important roles in host defense against invasive pathogens.