BTD-1, BTD-3, BTD-4 and BTD-7 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-3 is more effective against E.coli than BTD-1, BTD-4 and BTD-7. BTD-1 is a cyclic heterodimer composed of subunits A and B; disulfide-linked. BTD-3 is a cyclic homodimer composed of two subunits A; disulfide-linked. BTD-4 is a cyclic heterodimer composed of subunits A and C; disulfide-linked. BTD-7 is a cyclic heterodimer composed of subunits A and D; disulfide-linked. Forms a cyclic peptide with subunit B (BTD-1), subunit A (BTD-3), subunit C (BTD-4), or subunit D (BTD-7). An additional intersubunit disulfide bond is formed. BTD-1, heterodimer, cyclized. BTD-3, homodimer, cyclized. BTD-4, heterodimer, cyclized. BTD-7, heterodimer, cyclized. Belongs to the alpha-defensin family. Theta subfamily.