Flavins are notoriously photolabile, but while the photoproducts derived from the iso-alloxazine ring are well known the other photoproducts are not. In the case of FAD, typically the main cellular flavin, the other photoproducts are predicted to include four- and five-carbon sugars linked to ADP. These FAD photoproducts were shown to be potent glycating agents, more so than ADP-ribose. Such toxic compounds would require disposal via an ADP-sugar diphosphatase or other route. Comparative analysis of bacterial genomes uncovered a candidate disposal gene that is chromosomally clustered with genes for FAD synthesis or transport and is predicted to encode a protein of the PhnP cyclic phosphodiesterase family. The representative PhnP family enzyme from Koribacter versatilis (here named Fpd, FAD photoproduct diphosphatase) was found to have high, Mn2+-dependent diphosphatase activity against FAD photoproducts, FAD, and ADP-ribose, but almost no phosphodiesterase activity against riboflavin 4′,5′-cyclic phosphate, a chemical breakdown product of FAD. To provide a structural basis of the unique Fpd activity, the crystal structure of K. versatilis Fpd was determined. The results place Fpd in the broad metallo-β-lactamase-like family of hydrolases, a diverse family commonly using two metals for hydrolytic catalysis. The active site of Fpd contains two Mn2+ ions and a bound phosphate, consistent with a diphosphatase mechanism. Our results characterize the first PhnP family member that is a diphosphatase rather than a cyclic phosphodiesterase and suggest its involvement in a cellular damage-control system that efficiently hydrolyzes the reactive, ADP-ribose-like products of FAD photodegradation.
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January 2018
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A 3D representation of the filamentous cyanobacteria Anabaena. In this issue, Sein-Echaluce et al. report on the molecular basis for the integration of environmental signals by FurB from Anabaena sp. PCC 7120; for details see pages 151–168.
Research Article|
January 11 2018
An unusual diphosphatase from the PhnP family cleaves reactive FAD photoproducts
Guillaume A.W. Beaudoin;
Guillaume A.W. Beaudoin
*
1Horticultural Sciences Department, University of Florida, Gainesville, FL, U.S.A.
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Qiang Li;
Qiang Li
*
2Department of Chemistry, University of Florida, Gainesville, FL, U.S.A.
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Steven D. Bruner;
Steven D. Bruner
2Department of Chemistry, University of Florida, Gainesville, FL, U.S.A.
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Andrew D. Hanson
1Horticultural Sciences Department, University of Florida, Gainesville, FL, U.S.A.
Correspondence: Andrew D. Hanson ([email protected])
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Publisher: Portland Press Ltd
Received:
October 20 2017
Revision Received:
December 02 2017
Accepted:
December 07 2017
Accepted Manuscript online:
December 11 2017
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© 2018 The Author(s). Published by Portland Press Limited on behalf of the Biochemical Society
2018
Biochem J (2018) 475 (1): 261–272.
Article history
Received:
October 20 2017
Revision Received:
December 02 2017
Accepted:
December 07 2017
Accepted Manuscript online:
December 11 2017
Citation
Guillaume A.W. Beaudoin, Qiang Li, Steven D. Bruner, Andrew D. Hanson; An unusual diphosphatase from the PhnP family cleaves reactive FAD photoproducts. Biochem J 15 January 2018; 475 (1): 261–272. doi: https://doi.org/10.1042/BCJ20170817
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