The human beta-defensin-1 and alpha-defensins are encoded by adjacent genes: two peptide families with differing disulfide topology share a common ancestry.
We cloned a novel human beta-defensin gene and determined its full-length cDNA sequence. The entire gene spanned more than 7 kb and included a large 6962-bp intron. The 362-bp cDNA encoded a prepropeptide that corresponded precisely to the recently identified human beta-defensin HBD-1, an antimicrobial peptide implicated in the resistance of epithelial surfaces to microbial colonization. By two-color fluorescence in situ hybridization on both metaphase chromosome and released chromatin fiber, HBD-1 gene (DEFB1 in HUGO/GDB nomenclature) mapped to chromosomal region 8p23.1-p23.2 in close proximity (within 100-150 kb) to the gene for the human neutrophil alpha-defensin HNP-1 (DEFA1). Thus, despite a complete lack of DNA sequence similarity and despite differences in their disulfide-pairing pattern, the alpha- and beta-families appear to have evolved from a common premammalian defensin gene.