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Protein Sci. 2018 Oct 19. doi: 10.1002/pro.3529. [Epub ahead of print]

Crystal structure of AdoMet radical enzyme 7-carboxy-7-deazaguanine synthase from Escherichia coli suggests how modifications near [4Fe-4S] cluster engender flavodoxin specificity.

Author information

1
Department of Chemistry.
2
Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, 02139, United States.
3
Howard Hughes Medical Institute.
4
Department of Chemistry, University of Utah, Salt Lake City, Utah, 84112, United States.

Abstract

7-carboxy-7-deazaguanine synthase, QueE, catalyzes the radical mediated ring contraction of 6-carboxy-5,6,7,8-tetrahydropterin, forming the characteristic pyrrolopyrimidine core of all 7-deazaguanine natural products. QueE is a member of the S-adenosyl-L-methionine (AdoMet) radical enzyme superfamily, which harnesses the reactivity of radical intermediates to perform challenging chemical reactions. Members of the AdoMet radical enzyme superfamily utilize a canonical binding motif, a CX3 CXφC motif, to bind a [4Fe-4S] cluster and a partial (β/α)6 TIM barrel fold for the arrangement of AdoMet and substrates for catalysis. Although variations to both the cluster-binding motif and the core fold have been observed, visualization of drastic variations in the structure of QueE from Burkholderia multivorans called into question whether a re-haul of the defining characteristics of this superfamily was in order. Surprisingly, the structure of QueE from Bacillus subtilis revealed an architecture more reminiscent of the classical AdoMet radical enzyme. With these two QueE structures revealing varying degrees of alterations to the classical AdoMet fold, a new question arises: what is the purpose of these alterations? Here, we present the structure of a third QueE enzyme from Escherichia coli, which establishes the middle range of the spectrum of variation observed in these homologs. With these three homologs we compare and contrast the structural architecture and make hypotheses about the role of structural variations in binding and recognizing the biological reductant, flavodoxin. This article is protected by copyright. All rights reserved.

KEYWORDS:

AdoMet radical enzymes; Flavodoxin; flavin mononucleotide; iron-sulfur clusters; physiological reductant

PMID:
30341796
DOI:
10.1002/pro.3529

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