PhTD-1 has antimicrobial activity. In low salt conditions PhTD-1 has antibacterial activity against the Gram-negative bacterium E.coli ML35p (MIC=1.5 uM), the Gram-positive bacteria L.monocytogenes EGD (MIC=1.6 uM) and methicillin-resistant S.aureus ATCC 33591 (MIC=2.5 uM), and the fungus C.albicans 820 (MIC=1.6 uM). At high physiological salt concentrations the antimicrobial activity of PhTD-1 decreases slightly: E.coli ML35p (MIC=2.0 uM), L.monocytogenes EGD (MIC=1.7 uM), S.aureus ATCC 33591 (MIC=3.6 uM), and C.albicans 820 (MIC=6.5 uM). PhTD-1 is a cyclic heterodimer composed of subunits A and B; disulfide-linked. Forms a cyclic peptide with subunit A (PhTD-1). An additional intersubunit disulfide bond is formed. PhTD-1, heterodimer, cyclized. Belongs to the alpha-defensin family. Theta subfamily.