Closed fumarase C active‐site structures reveal SS Loop residue contribution in catalysis

Fumarase C (FumC) catalyzes the reversible conversion of fumarate to S‐malate. Previous structural investigations within the superfamily have reported a dynamic structural segment, termed the SS Loop. To date, active‐site asymmetry has raised the question of how SS Loop placement affects participati...

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Bibliographic Details
Published in:FEBS letters 2020-01, Vol.594 (2), p.337-357
Main Authors: Stuttgen, Gage M., Grosskopf, Julian D., Berger, Colton R., May, John F., Bhattacharyya, Basudeb, Weaver, Todd M.
Format: Article
Language:English
Subjects:
circular dichroism
fumarase
fumarate hydratase
Krebs cycle
metabolism
X‐ray crystallography
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Summary:Fumarase C (FumC) catalyzes the reversible conversion of fumarate to S‐malate. Previous structural investigations within the superfamily have reported a dynamic structural segment, termed the SS Loop. To date, active‐site asymmetry has raised the question of how SS Loop placement affects participation of key residues during the reaction. Herein, we report structural and kinetic analyses from Escherichia coli FumC variants to understand the contribution of SS Loop residues S318, K324, and N326. High‐resolution X‐ray crystallographic results reveal three distinct FumC active‐site conformations; disordered‐open, ordered‐open, and the newly discovered ordered‐closed. Surprisingly, each SS Loop variant has unaffected Michaelis constants coupled to reductions in turnover number. Based upon our structural and functional analyses, we propose structural and catalytic roles for each of the aforementioned residues.
ISSN:0014-5793
1873-3468
DOI:10.1002/1873-3468.13603