Evolution
Ostriches have a genome containing the gene coding for the antimicrobial peptide, Ostricacin-1. The presence of this peptide indicate that the genes coding for β-defensins have existed for a long time. Ostrich and other ratite species are related to Palaeognathiformes, which is the oldest order of birds living today.
β-defensins genes are found in the genome of both ostrich and mammalians. The genes coding for β-defensins could originate from genes which existed prior diversification of the avian and the mammalian line, which occurred for around 150 million years ago.
The fact that alpha and theta defensins are absence in older vertebrates, like birds and fishes, indicates that defensins must have evolved from the same ancestral gene coding for β-defensins.
Hoover et al (2001) showed that the origin of defensins were molecules similar to β-defensins which are found today, by comparing the amino acids and structures of the origin of β-defensins with β-defensins from insects and α-defensins found in mammalians. The β-defensins found in insects were actually more similar to the origin of defensins compared to α-defensins found in mammalians. The insects lines have been around for a longer time compared to mammalian lines, which suggest that the ancestor of the genes coding for defensins have existed for a long time.
The first human beta-defensin, HBD1, was discovered in 1995, followed by the HBD2 in 1997.
Read more about this topic: Beta Defensin
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