Inhibition of the Intrinsic NAD+ Glycohydrolase Activity of CD38 by Carbocyclic NAD Analogues

Carba-NAD and pseudocarba-NAD are carbocyclic analogues of NAD+ in which a 2,3-dihydroxycyclopentane methanol replaces the beta-d-ribonucleotide ring of the nicotinamide riboside moiety of NAD+ [Slama and Simmons (1988) Biochemistry 27, 183-193]. These carbocyclic NAD+ analogues, related to each other as diastereomers, have been tested as inhibitors of the intrinsic NAD+ glycohydrolase activity of human CD38, dog spleen NAD+ glycohydrolase, mouse CD38 and Aplysia californica cADP-ribose synthetase. Pseudocarba-NAD, the carbocyclic dinucleotide in which l-2,3-dihydroxycyclopentane methanol replaces the d-ribose of the nicotinamide riboside moiety of NAD+, was found to be the more potent inhibitor. Pseudocarba-NAD was shown to inhibit the intrinsic NAD+ glycohydrolase activity of human CD38 competitively, with Ki=148 microM determined for the recombinant extracellular protein domain and Ki=180 microM determined for the native protein expressed as a cell-surface enzyme on cultured Jurkat cells. Pseudocarba-NAD was shown to be a non-competitive inhibitor of the purified dog spleen NAD+ glycohydrolase, with Kis=47 miroM and Kii=198 microM. Neither pseudocarba-NAD nor carba-NAD inhibited mouse CD38 or Aplysia californica cADP-ribose synthetase significantly at concentrations up to 1 mM. The results underscore significant species differences in the sensitivity of these enzymes to inhibition, and indicate that pseudocarba-NAD will be useful as an inhibitor of the enzymic activity of human but not mouse CD38 in studies using cultured cells.