Porcine CD38 exhibits prominent secondary NAD+ cyclase activity

Abstract

Cyclic ADP-ribose (cADPR) mobilizes intracellular Ca2+ stores and activates Ca2+ influx to regulate a wide range of physiological processes. It is one of the products produced from the catalysis of NAD+ by the multifunctional CD38/ADP-ribosyl cyclase superfamily. After elimination of the nicotinamide ring by the enzyme, the reaction intermediate of NAD+ can either be hydrolyzed to form linear ADPR or cyclized to form cADPR. We have previously shown that human CD38 exhibits a higher preference towards the hydrolysis of NAD+ to form linear ADPR while Aplysia ADP-ribosyl cyclase prefers cyclizing NAD+ to form cADPR. In this study, we characterized the enzymatic properties of porcine CD38 and revealed that it has a prominent secondary NAD+ cyclase activity producing cADPR. We also determined the X-ray crystallographic structures of porcine CD38 and were able to observe conformational flexibility at the base of the active site of the enzyme which allow the NAD+ reaction intermediate to adopt conformations resulting in both hydrolysis and cyclization forming linear ADPR and cADPR respectively.