Gallinacin-3, an inducible epithelial beta-defensin in the chicken

Gallinacin-3 and gallopavin-1 (GPV-1) are newly characterized, epithelial beta-defensins of the chicken (Gallus gallus) and turkey (Meleagris gallopavo), respectively. In normal chickens, the expression of gallinacin-3 was especially prominent in the tongue, bursa of Fabricius, and trachea. It also occurred in other organs, including the skin, esophagus, air sacs, large intestine, and kidney. Tracheal expression of gallinacin-3 increased significantly after experimental infection of chickens with Haemophilus paragallinarum, whereas its expression in the tongue, esophagus, and bursa of Fabricius was unaffected. The precursor of gallinacin-3 contained a long C-terminal extension not present in the prepropeptide. By comparing the cDNA sequences of gallinacin-3 and GPV-1, we concluded that a 2-nucleotide insertion into the gallinacin-3 gene had induced a frameshift that read through the original stop codon and allowed the chicken propeptide to lengthen. The striking structural resemblance of the precursors of beta-defensins to those of crotamines (highly toxic peptides found in rattlesnake venom) supports their homology, even though defensins are specialized to kill microorganisms and crotamines are specialized to kill much larger prey.