ESSENTIAL CYSTEINE RESIDUES FOR CYCLIC ADP-RIBOSE SYNTHESIS AND HYDROLYSIS BY CD38

We have recently demonstrated that cyclic ADP-ribose (cADPR) serves as a second messenger for glucose-induced insulin secretion (Takasawa, S ., Nata, K., Yonekura, H., and Okamoto, H. (1993) Science 259, 370-373 ) and that human leukocyte antigen CD38 has both ADP-ribosyl cyclase a nd cADPR hydrolase activities (Takasawa, S., Tohgo, A., Noguchi, N., K oguma, T., Nata, K., Sugimoto, T., Yonekura, Il., and Okamoto, H. (199 3) J. Biol. Chem. 268, 26052-26054). Although the amino acid sequence of Aplysia ADP-ribosyl cyclase exhibits a high degree of amino acid se quence identity with that of CD38, the Aplysia enzyme shows only ADP-r ibosyl cyclase but not cADPR hydrolase. In the present study, me intro duced site-directed mutations to CD38 and found that C119K- and/or C20 1E-CD38 exhibited only ADP-ribosyl cyclase activity. Furthermore, Aply sia ADP-ribosyl cyclase into which we introduced the mutations K95C an d E176C, which correspond to residues 119 and 201 of human CD38, exhib ited not only ADP-ribosyl cyclase activity but also cADPR hydrolase. T hese results indicate that cysteine residues 119 and 201 in CD38 have crucial roles in the synthesis and hydrolysis of cADPR.