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Journal of Bacteriology, February 2008, p. 1108-1117, Vol. 190, No. 3
0021-9193/08/$08.00+0     doi:10.1128/JB.01522-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Structural Basis for Different Substrate Specificities of Two ADP-Ribose Pyrophosphatases from Thermus thermophilus HB8{triangledown}

Taisuke Wakamatsu,1 Noriko Nakagawa,2,3 Seiki Kuramitsu,1,2,3 and Ryoji Masui2,3*

Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan,1 Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan,2 RIKEN SPring-8 Center, Harima Institute, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan3

Received 20 September 2007/ Accepted 12 November 2007

ADP-ribose (ADPR) is one of the main substrates of Nudix proteins. Among the eight Nudix proteins of Thermus thermophilus HB8, we previously determined the crystal structure of Ndx4, an ADPR pyrophosphatase (ADPRase). In this study we show that Ndx2 of T. thermophilus also preferentially hydrolyzes ADPR and flavin adenine dinucleotide and have determined its crystal structure. We have determined the structures of Ndx2 alone and in complex with Mg2+, with Mg2+ and AMP, and with Mg2+ and a nonhydrolyzable ADPR analogue. Although Ndx2 recognizes the AMP moiety in a manner similar to those for other ADPRases, it recognizes the terminal ribose in a distinct manner. The residues responsible for the recognition of the substrate in Ndx2 are not conserved among ADPRases. This may reflect the diversity in substrate specificity among ADPRases. Based on these results, we propose the classification of ADPRases into two types: ADPRase-I enzymes, which exhibit high specificity for ADPR; and ADPRase-II enzymes, which exhibit low specificity for ADPR. In the active site of the ternary complexes, three Mg2+ ions are coordinated to the side chains of conserved glutamate residues and water molecules. Substitution of Glu90 and Glu94 with glutamine suggests that these residues are essential for catalysis. These results suggest that ADPRase-I and ADPRase-II enzymes have nearly identical catalytic mechanisms but different mechanisms of substrate recognition.

* Corresponding author. Mailing address: Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan. Phone: 81-6-6850-5434. Fax: 81-6-6850-5442. E-mail: rmasui{at}bio.sci.osaka-u.ac.jp

{triangledown} Published ahead of print on 26 November 2007.

Journal of Bacteriology, February 2008, p. 1108-1117, Vol. 190, No. 3
0021-9193/08/$08.00+0     doi:10.1128/JB.01522-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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