CRYSTAL-STRUCTURE OF APLYSIA ADP RIBOSYL CYCLASE, A HOMOLOG OF THE BIFUNCTIONAL ECTOZYME CD38

ADP ribosyl cyclase synthesizes the novel secondary messenger cyclic A DP ribose (cADPR) utilizing NAD as a substrate. The enzyme shares exte nsive sequence similarity with two lymphocyte antigens, CD38 and BST-l ,which hydrolyse as well as synthesize cADPR. The crystal structure pr ovides a model for these cell surface enzymes. Cyclase contains two sp atially separated pockets composed of sequence conserved residues, sug gesting that the cyclization reaction may entail use of distinct sites . The enzyme dimer encloses a cavity which may entrap the intermediate , ADP ribose.