Redox-dependent substrate-cofactor interactions in the Michaelis-complex of a flavin-dependent oxidoreductase

Enthalten in
Nature Communications 
Volume
8
Article Number
16084
Citation
Nature Communications (8): 16084 (2017-07-14)
Publisher DOI
10.1038/ncomms16084
Publisher
Nature Publishing Group UK
How an enzyme activates its substrate for turnover is fundamental for catalysis but incompletely understood on a structural level. With redox enzymes one typically analyses structures of enzyme-substrate complexes in the unreactive oxidation state of the cofactor, assuming that the interaction between enzyme and substrate is independent of the cofactors oxidation state. Here, we investigate the Michaelis complex of the flavoenzyme xenobiotic reductase A with the reactive reduced cofactor bound to its substrates by X-ray crystallography and resonance Raman spectroscopy and compare it to the non-reactive oxidized Michaelis complex mimics. We find that substrates bind in different orientations to the oxidized and reduced flavin, in both cases flattening its structure. But only authentic Michaelis complexes display an unexpected rich vibrational band pattern uncovering a strong donor-acceptor complex between reduced flavin and substrate. This interaction likely activates the catalytic ground state of the reduced flavin, accelerating the reaction within a compressed cofactor-substrate complex.
DDC Class
620: Ingenieurwissenschaften
Funding Organisations
Deutsche Forschungsgemeinschaft (DFG) 
More Funding Information
The Deutsche Forschungsgemeinschaft is acknowledged for funding of the project (EXC 314 ‘Unifying Concepts in Catalysis—UniCat’)