Structural Basis for the Mechanistic Understanding of Human CD38-controlled Multiple Catalysis

• Published in: The Journal of biological chemistry 2006-10, Vol.281 (43), p.32861-32869
• Main Authors: Liu, Qun, Kriksunov, Irina A., Graeff, Richard, Munshi, Cyrus, Lee, Hon Cheung, Hao, Quan
• Format: Article
• Language: English
• Subjects: ADP-ribosyl Cyclase 1 - chemistry; ADP-ribosyl Cyclase 1 - isolation & purification; ADP-ribosyl Cyclase 1 - metabolism; Amino Acid Substitution; Base Sequence; Binding Sites; Catalysis; Cold Temperature; Crystallography, X-Ray; Cyclic ADP-Ribose - metabolism; Dimerization; Enzyme Stability; Glutamic Acid - metabolism; Guanosine Diphosphate Sugars - metabolism; Humans; Hydrolysis; Hydrophobic and Hydrophilic Interactions; Kinetics; Models, Molecular; Molecular Sequence Data; NAD - metabolism; NAD+ Nucleosidase - metabolism; Sequence Homology, Nucleic Acid; Serine - metabolism; Static Electricity; Substrate Specificity; Water - chemistry
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M606365200

The enzymatic cleavage of the nicotinamide-glycosidic bond on nicotinamide adenine dinucleotide (NAD+) has been proposed to go through an oxocarbenium ion-like transition state. Because of the instability of the ionic intermediate, there has been no structural report on such a transient reactive species. Human CD38 is an ectoenzyme that can use NAD+ to synthesize two calcium-mobilizing molecules. By using NAD+ and a surrogate substrate, NGD+, we captured and determined crystal structures of the enzyme complexed with an intermediate, a substrate, and a product along the reaction pathway. Our results showed that the intermediate is stabilized by polar interactions with the catalytic residue Glu226 rather than by a covalent linkage. The polar interactions between Glu226 and the substrate 2′,3′-OH groups are essential for initiating catalysis. Ser193 was demonstrated to have a regulative role during catalysis and is likely to be involved in intermediate stabilization. In addition, a product inhibition effect by ADP-ribose (through the reorientation of the product) or GDP-ribose (through the formation of a covalently linked GDP-ribose dimer) was observed. These structural data provide insights into the understanding of multiple catalysis and clues for drug design.