BTD-1 and BTD-2 have antimicrobial activity against the Gram-negative bacterium E.coli ML35, the Gram-positive bacterium S.aureus 502a, and the fungus C.albicans 16820. BTD-2 is more effective against E.coli than BTD-1. BTD-1 is a cyclic heterodimer composed of subunits A and B; disulfide-linked. BTD-2 is a cyclic homodimer composed of two subunits B; disulfide-linked. Forms a cyclic peptide with subunit A (BTD-1), or subunit B (BTD-2). An additional intersubunit disulfide bond is formed. BTD-1, heterodimer, cyclized. BTD-2, homodimer, cyclized. Belongs to the alpha-defensin family. Theta subfamily.