To elucidate the structural features of the mussel defensin MGD1 required for antimicrobial activity, we synthesized a series of peptides corresponding to the main known secon-dary structures of the molecule and evaluated their activity towards Gram-positive and Gram-negative bacteria, and filamentous fungi. We found that the nonapeptide corres-ponding to residues 25–33 of MGD1 (CGGWHRLRC) exhibited bacteriostatic activity once it was cyclized by a non-naturally occurring disulfide bridge.
