Abstract
Metalloproteins catalyze a range of reactions, with enhanced chemical functionality due to their metal cofactor. The reaction mechanisms of metalloproteins have been experimentally characterized by spectroscopy, macromolecular crystallography and cryo-electron microscopy. An important caveat in structural studies of metalloproteins remains the artefacts that can be introduced by radiation damage. Photoreduction, radiolysis and ionization deriving from the electromagnetic beam used to probe the structure complicate structural and mechanistic interpretation. Neutron protein diffraction remains the only structural probe that leaves protein samples devoid of radiation damage, even when data are collected at room temperature. Additionally, neutron protein crystallography provides information on the positions of light atoms such as hydrogen and deuterium, allowing the characterization of protonation states and hydrogen-bonding networks. Neutron protein crystallography has further been used in conjunction with experimental and computational techniques to gain insight into the structures and reaction mechanisms of several transition-state metal oxidoreductases with iron, copper and manganese cofactors. Here, the contribution of neutron protein crystallography towards elucidating the reaction mechanism of metalloproteins is reviewed.
Highlights
Metals play a central role in biology, in association with the proteome, where they have catalytic, electron-transfer, structural and storage roles (Holm et al, 1996)
The authors conclude that the observed protonation states in the Achromobacter cycloclastes CuNiR (AcNiR) active site support the hypothesis that upon binding of the nitrite substrate and displacement of the axial water ligand, protonation of AspCAT is triggered via the bridging water
In their neutron diffraction structure, Murakawa and coworkers emphasize the capability of neutron diffraction to reveal new and exciting conformations by presenting evidence for a triply shared proton between trihydroxyphenylalanine quinone (TPQ) and the conserved aspartic acid residue Asp298 in a trifurcated hydrogen bond identified by a positive neutron scattering-length density (NSLD) difference density peak
Summary
Metals play a central role in biology, in association with the proteome, where they have catalytic, electron-transfer, structural and storage roles (Holm et al, 1996). The reaction mechanism of metalloproteins has been explored using a plethora of techniques including structural, spectroscopic and computational studies (Fontecilla-Camps & Nicolet, 2014). To gain a more complete understanding of protein interactions and catalysis, a complete, all-atom structure is a requisite. Neutron protein crystallography remains the sole structural technique that can determine H-atom positions without radiation-induced damage both at room temperature and under cryo-conditions, making it valuable for the study of metalloproteins and their reaction mechanisms (Bodenheimer et al, 2017; Meilleur et al, 2018, 2020; Ashkar et al, 2018)
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