Structural highlights
FunctionCD38_HUMAN Synthesizes cyclic ADP-ribose, a second messenger for glucose-induced insulin secretion. Also has cADPr hydrolase activity. Also moonlights as a receptor in cells of the immune system. Publication Abstract from PubMedhCD157 catalyzes the hydrolysis of nicotinamide riboside (NR) and nicotinic acid riboside (NAR). The release of nicotinamide or nicotinic acid from NR or NAR was confirmed by spectrophotometric, HPLC and NMR analyses. hCD157 is inactivated by a mechanism-based inhibitor, 2'-deoxy-2'-fluoro-nicotinamide arabinoside (fNR). Modification of the enzyme during the catalytic cycle by NR, NAR, or fNR increased the intrinsic protein fluorescence by approximately 50%. Pre-steady state and steady state data were used to derive a minimal kinetic scheme for the hydrolysis of NR. After initial complex formation a reversible step (360 and 30s-1) is followed by a slow irreversible step (0.1s-1) that defined the rate limiting step, or kcat. The calculated KMapp value for NR in the hydrolytic reaction is 6nM. The values of the kinetic constants suggest that one biological function of cell-surface hCD157 is to bind and slowly hydrolyze NR, possibly converting it to a ligand-activated receptor. Differences in substrate preference between hCD157 and hCD38 were rationalized through a comparison of the crystal structures of the two proteins. This comparison identified several residues in hCD157 (F108 and F173) that can potentially hinder the binding of dinucleotide substrates (NAD+). A pre-steady state and steady state kinetic analysis of the N-ribosyl hydrolase activity of hCD157.,Preugschat F, Carter LH, Boros EE, Porter DJ, Stewart EL, Shewchuk LM Arch Biochem Biophys. 2014 Sep 20. pii: S0003-9861(14)00342-7. doi:, 10.1016/j.abb.2014.09.008. PMID:25250980[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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