Cathelicidin structure. A) Cathelicidin genes are approximately 2 kilobases in size with a conserved four exon – three intron arrangement. Exons one, two and three code for the highly conserved N-terminal-coding region of the precursor protein known as the cathelin domain. Exon four codes for a highly variable domain with antimicrobial properties in the mature peptide. B) Alignment of bovine cathelicidin precursor proteins with those from human (Homo sapiens, hCAP-18), mouse (Mus musculus, CAMP), horse (Equus caballus, ecath-2), dog (Canis lupus familiaris, CAMP) and chicken (Gallus gallus, cathl2). (See Additional file 1 for details of the mature peptide encoded by each cathelicidin gene.) Conserved residues are indicated by the asterisk. Exons 1-3 are highly conserved between species with considerable variation in sequence within the exon 4 sequence within and between species. These peptides contain two disulfide bonds between cysteine residues C85-C96 and C107-C124.