ADP-Ribosyl Cyclase: Crystal Structures Reveal a Covalent Intermediate

• Published in: Structure (London) 2004-03, Vol.12 (3), p.477-486
• Main Authors: Love, Michael L, Szebenyi, Doletha M.E, Kriksunov, Irina A, Thiel, Daniel J, Munshi, Cyrus, Graeff, Richard, Lee, Hon Cheung, Hao, Quan
• Format: Article
• Language: English
• Subjects: ADP-ribosyl Cyclase - chemistry; ADP-ribosyl Cyclase - metabolism; Amino Acid Sequence; Animals; Aplysia - enzymology; Conserved Sequence; Crystallography, X-Ray; Molecular Sequence Data; Nicotinamide Mononucleotide - metabolism; Protein Structure, Secondary; Protein Structure, Tertiary; Ribosemonophosphates - metabolism; Sequence Alignment
• ISSN: 0969-2126; 1878-4186
• DOI: 10.1016/j.str.2004.02.006

ADP-ribosyl cyclase catalyzes the elimination of nicotinamide from NAD and cyclization to cADPR, a known second messenger in cellular calcium signaling pathways. We have determined to 2.0 Å resolution the structure of Aplysia cyclase with ribose-5-phosphate bound covalently at C3′ and with the base exchange substrate (BES), pyridylcarbinol, bound to the active site. In addition, further refinement at 2.4 Å resolution of the structure of nicotinamide-bound cyclase, which was previously reported, reveals that ribose-5-phosphate is also covalently bound in this structure, and a second nicotinamide site was identified. The structures of native and mutant Glu179Ala cyclase were also solved to 1.7 and 2.0 Å respectively. It is proposed that the second nicotinamide site serves to promote cyclization by clearing the active site of the nicotinamide byproduct. Moreover, a ribosylation mechanism can be proposed in which the cyclization reaction proceeds through a covalently bound intermediate.