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Published online on May 5, 2008
Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0802535105


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BIOCHEMISTRY
Structural insight into signal conversion and inactivation by NTPDase2 in purinergic signaling

Matthias Zebisch and Norbert Sträter*

Center for Biotechnology and Biomedicine, Institute of Bioanalytical Chemistry, Faculty of Chemistry and Mineralogy, University of Leipzig, Deutscher Platz 5, 04103 Leipzig, Germany

Communicated by William N. Lipscomb, Harvard University, Cambridge, MA, March 13, 2008 (received for review January 4, 2008)

Abstract

Cell surface-located nucleoside triphosphate diphosphohydrolases (NTPDase1, -2, -3, and -8) are oligomeric integral membrane proteins responsible for signal conversion and inactivation in extracellular nucleotide-mediated "purinergic" signaling. They catalyze the sequential hydrolysis of the signaling molecule ATP via ADP to AMP. Here we present the structure of the extracellular domain of Rattus norvegicus NTPDase2 in an active state at resolutions between 1.7 Å and 2.1 Å in four different forms: (i) apo form, (ii) ternary complex with the nonhydrolyzable ATP analog AMPPNP and cofactor Ca2+, (iii) quaternary complex with Ca2+ and bound products AMP and phosphate, and (iv) binary product complex with AMP only. Analysis of the ATP (analog) binding mode explains the importance of several residues for activity and allows suggestion of a catalytic mechanism. The carboxylate group of E165 serves as a catalytic base and activates a water molecule, which is well positioned for nucleophilic attack on the terminal phosphate. Based on analysis of the two product complex structures in which AMP adopts different conformations, a substrate binding mode for ADP hydrolysis is proposed. This allows for an understanding of how the same hydrolytic site can be engaged in ATP and ADP but not AMP hydrolysis.

ATP hydrolysis | CD39-like | ecto-enzyme | membrane protein | x-ray structure

Footnotes

Author contributions: N.S. designed research; M.Z. performed research; M.Z. and N.S. analyzed data; and M.Z. wrote the paper.

The authors declare no conflict of interest.

*To whom correspondence should be addressed. E-mail: strater{at}bbz.uni-leipzig.de

© 2008 by The National Academy of Sciences of the USA


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