Three-dimensional Structure of Abrin-a A-chain Having Ribosome Inactivating Activity

Abstract

Three-dimensional structure of abrin-a A-chain has been solved by X-ray crystal structure analysis. The protein is a member of the Type II ribosome inactivating proteins (RIPs) which catalyze endohydrolysis of the N-glycosidic bond of a particular adenosine at position 4, 324 in 28S rRNA and thereby inhibit protein syntheses occurring on ribosome particles. It turned out that this enzyme had a similar three-dimensional structure to that of the A-chain of ricin, the crystal structure of which has been established before. The structure of abrin-a A-chain is composed of three domains, Domains 1, 2 and 3. The active site is located in the cleft which is surrounded by the surfaces of Domains 1, 2 and 3. The size of the cleft seems to be sufficient for recognizing RNA fragments including the GAGA tetraloop.