Recent structural studies of peptides in Japan

Recent x-ray structure analyses of peptides in Japan were reviewed. A series of peptides containing an aminoisobutyric acid (Aib) residue was analyzed and their helical types were investigated. Two convenient methods to determine helical types were obtained. One method was obtained by calculating averaged helical parameters and the other was obtained by investigating meridional intensity distributions. The conformations of some peptides, such as aureobasidin E, ascidiacyclamide, synthetic analogues of heat-stable enterotoxin, were studied by an x-ray diffraction method, and in some cases, with the help of nmr spectroscopy and molecular mechanics calculations. Since these peptides have physiologically important activities, the structure-activity relationships of these peptides were discussed. Several other peptide structures and the polymorphism of amino acids are also reported.