3D Structure of Antimicrobial Peptides 1. Structure annotation The information on the three-dimensional (3D) structure of antimicrobial peptides is annotated in this database from the first version of the APD (Wang & Wang, 2004).It includes methods for structural determination, structural class, structural regions, critical residues, and the type of membrane-mimetic environments.. Structural statistics of antimicrobial peptides A list of antimicrobial peptdes with a defined 3D structure can be obtained by searching the APD database. The statistics of a variety of structures is also provided in this database. Go to the Statistic Interface.