The three-dimensional solution structure ofAesculus hippocastanum antimicrobial protein 1 determined by1H nuclear magnetic resonance

Aesculus hippocastanum antimi- crobial protein 1 (Ah-AMP1) is a plant defensin isolated from horse chestnuts. The plant defensins have been divided in several subfamilies according to their amino acid sequence homology. Ah-AMP1, belonging to subfamily A2, inhibits growth of a broad range of fungi. So far, a three-dimensional structure has been determined only for members of subfamilies A3 and B2. In order to understand activ- ity and specificity of these plant defensins, the structure of a protein belonging to subfamily A2 is needed. We report the three-dimensional solution structure of Ah-AMP1 as determined from two- dimensional 1 H nuclear magnetic resonance data. The structure features all the characteristics of the ''cysteine-stabilized ab-motif.'' A comparison of the structure, the electrostatic potential surface and regions important for interaction with the fungal receptor, is made with Rs-AFP1 (plant defensin of subfamily A3). Thus, residues important for activity and specificity have been assigned. Proteins 1999;37:388-403. r 1999 Wiley-Liss, Inc.