Cathelicidins are a kind of cationic host defense peptides of the innate immunity and are widespread in mammals and also found in other species such as fishes and birds. Their structure comprises a conserved prepropiece and an antimicrobial domain that is structurally varied both intra- and inter-species. Three cDNA sequences coding for elapid cathelicidins were first cloned from constructed venom gland cDNA libraries of Naja atra, Bungarus fasciatus and Ophiophagus hannah, respectively. The open reading frames of the cloned elapid cathelicidins were all composed of 576 bp and coded for 191 amino acid residue protein precursors. Each of the deduced elapid cathelicidin has a 22 amino-acid-residue signal peptide, a conserved cathelin domain of 135 amino acid residues and a mature antimicrobial peptide of 34 amino acid residues. Unlike the highly divergent cathelicidins in mammals, the nucleotide and deduced protein sequences of the three cloned elapid cathelicidins were comparatively conserved. All the elapid mature cathelicidins were predicted to be cleaved at Valine157 by elastase. One of the deduced mature cathelicidins (OH-CATH), originated from king cobra, was chemically synthesized and it showed strong antibacterial activity against various tested bacteria with MICs of 1-20 g/ml in the presence of 1% NaCl. Meanwhile, the synthesized peptide showed no haemolytic activity toward human red blood cells even at a high dose of 200 g/ml. Phylogenetic analysis of cathelicidins from vertebrate suggested that elapid and viperid cathelicidins were grouped together in the tree. Snake cathelicidins were evolutionary more closely related to the neutrophilic granule proteins (NGPs) from mouse, rat and rabbit. Elapid cathelicidins might be served as a good model for the developing of novel therapeutic drugs.
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