Multiple States of Nitrile Hydratase from Rhodococcus equi TG328-2: Structural and Mechanistic Insights from Electron Paramagnetic Resonance and Density Functional Theory Studies

Authors

Natalia Stein, University of Wisconsin - MilwaukeeFollow
Natalie Gumataotao, Loyola University Chicago
Natalia Hajnas, Loyola University Chicago
Rui Wu, Loyola University Chicago
Karunagala Pathiranage Wasantha Lankathilaka, Marquette UniversityFollow
Uwe Bornscheuer, Greifswald University
Dali Liu, Loyola University ChicagoFollow
Adam T. Fiedler, Marquette UniversityFollow
Richard C. Holz, Marquette UniversityFollow
Brian Bennett, Marquette UniversityFollow

Document Type

Article

Language

eng

Publication Date

2017

Publisher

American Chemical Society

Source Publication

Biochemistry

Source ISSN

0006-2960

Abstract

Iron-type nitrile hydratases (NHases) contain an Fe(III) ion coordinated in a characteristic “claw setting” by an axial cysteine thiolate, two equatorial peptide nitrogens, the sulfur atoms of equatorial cysteine-sulfenic and cysteine-sulfinic acids, and an axial water/hydroxyl moiety. The cysteine-sulfenic acid is susceptible to oxidation, and the enzyme is traditionally prepared using butyric acid as an oxidative protectant. The as-prepared enzyme exhibits a complex electron paramagnetic resonance (EPR) spectrum due to multiple low-spin (S = ¹/₂) Fe(III) species. Four distinct signals can be assigned to the resting active state, the active state bound to butyric acid, an oxidized Fe(III)–bis(sulfinic acid) form, and an oxidized complex with butyric acid. A combination of comparison with earlier work, development of methods to elicit individual signals, and design and application of a novel density functional theory method for reproducing g tensors to unprecedentedly high precision was used to assign the signals. These species account for the previously reported EPR spectra from Fe-NHases, including spectra observed upon addition of substrates. Completely new EPR signals were observed upon addition of inhibitory boronic acids, and the distinctive g₁ features of these signals were replicated in the steady state with the slow substrate acetonitrile. This latter signal constitutes the first EPR signal from a catalytic intermediate of NHase and is assigned to a key intermediate in the proposed catalytic cycle. Earlier, apparently contradictory, electron nuclear double resonance reports are reconsidered in the context of this work.

Comments

Accepted version. Biochemistry, Vol. 56, No. 24 (2017): 3068-3077. DOI. © 2017 American Chemical Society. Used with permission.

Recommended Citation

Stein, Natalia; Gumataotao, Natalie; Hajnas, Natalia; Wu, Rui; Wasantha Lankathilaka, Karunagala Pathiranage; Bornscheuer, Uwe; Liu, Dali; Fiedler, Adam T.; Holz, Richard C.; and Bennett, Brian, "Multiple States of Nitrile Hydratase from Rhodococcus equi TG328-2: Structural and Mechanistic Insights from Electron Paramagnetic Resonance and Density Functional Theory Studies" (2017). Physics Faculty Research and Publications. 144.
https://epublications.marquette.edu/physics_fac/144