The known three-dimensional structure of human hemoglobin shows an alpha-helical region within the C-terminal part of the hemoglobin β-chain (PDB ID: 2HHB). The structure of this polypeptide

has given rise to the hypothesis that the antimicrobial mechanism of action resembles that of known peptides such as the magainins and defensins which permeabilize bacterial membranes ( Oren and Shai, 1998 and Brogden, 2005). The cytotoxicity of many antimicrobial peptides to mammalian cells greatly limits their use as therapeutics HKI-272 molecular weight (Rajanbabu and Chen, 2011). When tested on red blood cells and on microcirculation, PcfHb showed no hemolytic activity or tissue damage even at peptide concentrations of up to 100 μM. Moreover, a small pro-inflammatory response at the microcirculatory environment was seen indicating that PcfHb may have a potential protective activity being immunogenic to humans, not necessarily

in terms of antibody generation but as inflammation promoters and recruitment agents or immune enhancers (Otero-González et al., 2010). PcfHb could also be expected to function in conjunction with the histone-like proteins that were found in the same epithelial mucus in this stingray (data not shown), providing a strong line of innate host defence against eukaryotic as well as prokaryotic pathogens. Although innate immunity to microbial infection is a property common to almost all forms of life, it was quite unexpected that hemoglobin, one of the most well-characterized proteins GSK2126458 datasheet due to its function in oxygen transport, should contribute to innate immunity. However, recent studies have identified Hb-derived AMPs from humans and other animals; some of which were more inhibitory to eukaryotes than bacteria (Ullal et al., 2008 and Ullal

and Noga, 2010). In view of the fact that different hemoglobin-derived peptide fragments exhibit Orotidine 5′-phosphate decarboxylase diverse antibiotic activities, it is conceivable that, in addition to its role in oxygen transport hemoglobin functions as an important multi-defense agent against a wide range of microorganisms. In conclusion, we have shown for the first time that a protein with high sequence similarity to the hemoglobin β chain is an antimicrobial polypeptide naturally occurring in the mucus of stingrays. This finding is in accordance with the data of Parish et al. (2001) which identified the region containing the antimicrobial fragments at the amino acid sequences of free β -hemoglobin chain with a greater activity on gram-positive bacteria. Due to the broad antimicrobial action of PcfHb against Gram-positive and Gram-negative bacteria and yeast and its pro-inflammatory action, it may be suggested that this antimicrobial polypeptide could play a significant role in the innate immune response of this and other fishes.