Gallin; an antimicrobial peptide member of a new avian defensin family, the ovodefensins, has been subject to recent gene duplication

Abstract

BackgroundEgg white must provide nutrients and protection to the developing avian embryo. One way in which this is achieved is an arsenal of antimicrobial proteins and peptides which are essentially extensions of the innate immune system. Gallin is a recently identified member of a family of peptides that are found in egg white. The function of this peptide family has not been identified and they are potentially antimicrobial.ResultsWe have confirmed that there are at least 3 forms of the gallin gene in the chicken genome in 3 separate lines of chicken, all the forms are expressed in the tubular cells of the magnum region of the oviduct, consistent with its presence in egg white. mRNA expression levels are in the order 10,000 times greater in the magnum than the shell gland. The conservation between the multiple forms of gallin in the chicken genome compared with the conservation between gallin and other avian gallin like peptides, suggests that the gene duplication has occurred relatively recently in the chicken lineage. The gallin peptide family contains a six cysteine motif (C-X5-C-X3-C-X11-C-X3-C-C) found in all defensins, and is most closely related to avian beta-defensins, although the cysteine spacing differs. Further support for the classification comes from the presence of a glycine at position 10 in the 41 amino acid peptide. Recombinant gallin inhibited the growth of Escherischia coli (E. coli) at a concentration of 0.25 μM confirming it as part of the antimicrobial innate immune system in avian species.ConclusionsThe relatively recent evolution of multiple forms of a member of a new defensin related group of peptides that we have termed ovodefensins, may be an adaptation to increase expression or the first steps in divergent evolution of the gene in chickens. The potent antimicrobial activity of the peptide against E. coli increases our understanding of the antimicrobial strategies of the avian innate immune system particularly those of the egg white and the evolution of the defensin family. The potential of this peptide and others in the family can now be investigated in a number of novel antimicrobial roles.

Three-dimensional NMR Structure of Hen Egg Gallin (Chicken Ovodefensin) Reveals a New Variation of the β-Defensin Fold

“…Two other related peptides, dBPS1 and dBPS2, were also found in duck egg white (33). Their cysteine spacing (CX 3-5 CX 3 CX 11 C 3-4 CC) provides evidence that they are related to defensins, but the gallin gene does not belong to the cluster of AvBD genes, and its primary structure differs from typical AvBD sequences (34). This new subfamily of defensins was therefore termed ovodefensins.…”

“…This new subfamily of defensins was therefore termed ovodefensins. In view of the slight difference in cysteine spacing, it has been proposed that ovodefensins and avian defensins may have diverged from a common ancestor (34). Interestingly, gallin is potentially coded by three different genes (34), which are clustered on chromosome 3 and separated from the cluster of AvBD genes.…”

“…In view of the slight difference in cysteine spacing, it has been proposed that ovodefensins and avian defensins may have diverged from a common ancestor (34). Interestingly, gallin is potentially coded by three different genes (34), which are clustered on chromosome 3 and separated from the cluster of AvBD genes. To date, the ovodefensin subfamily counts seven members, including the two sequences, taeniopygin-1 and taeniopygin-2, predicted from the zebra finch genome (34).…”

“…Interestingly, gallin is potentially coded by three different genes (34), which are clustered on chromosome 3 and separated from the cluster of AvBD genes. To date, the ovodefensin subfamily counts seven members, including the two sequences, taeniopygin-1 and taeniopygin-2, predicted from the zebra finch genome (34). Besides the classical members of the ovodefensin subfamily, it is noteworthy that the cysteine spacings of dBPS1 and taeniopygin-2 are slightly different and were first described as "related to ovodefensins" (34).…”

Scientific Opinion on the public health risks of table eggs due to deterioration and development of pathogens

“…The antimicrobial activity of egg albumen is well documented (see Baron et al (2010) and Guyot et al (2013) for reviews) and it serves as a protective barrier because of its viscosity, which impairs bacterial motility, its alkaline pH (around 9.3, attained within days of lay), and its nutritional deficiencies, especially available iron restriction. Egg albumen also contains an arsenal of antimicrobial molecules, including proteins (Table 3), peptides (Gong et al, 2010;Hervé-Grépinet et al, 2010) and antibodies. Lysozyme is a well-known inhibitory protein, expressing muramidase activity against gram-positive bacteria.…”