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Structural studies of the unusual metal-ion site of the GH124 endoglucanase from Ruminiclostridium thermocellum

Lookup NU author(s): Dr Alan Cartmell

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Abstract

© 2018 International Union of Crystallography. The recent discovery of 'lytic' polysaccharide monooxygenases, copperdependent enzymes for biomass degradation, has provided new impetus for the analysis of unusual metal-ion sites in carbohydrate-active enzymes. In this context, the CAZY family GH124 endoglucanase from Ruminiclostridium thermocellum contains an unusual metal-ion site, which was originally modelled as a Ca2+ site but features aspartic acid, asparagine and two histidine imidazoles as coordinating residues, which are more consistent with a transition-metal binding environment. It was sought to analyse whether the GH124 metal-ion site might accommodate other metals. It is demonstrated through thermal unfolding experiments that this metal-ion site can accommodate a range of transition metals (Fe2+, Cu2+, Mn2+ and Ni2+), whilst the three-dimensional structure and mass spectrometry show that one of the histidines is partially covalently modified and is present as a 2-oxohistidine residue; a feature that is rarely observed but that is believed to be involved in an 'off-switch' to transition-metal binding. Atomic resolution (<1.1 A ° ) complexes define the metal-ion site and also reveal the binding of an unusual fructosylated oligosaccharide, which was presumably present as a contaminant in the cellohexaose used for crystallization. Although it has not been possible to detect a biological role for the unusual metal-ion site, this work highlights the need to study some of the many metal-ion sites in carbohydrate-active enzymes that have long been overlooked or previously mis-assigned.


Publication metadata

Author(s): Urresti S, Cartmell A, Liu F, Walton PH, Davies GJ

Publication type: Article

Publication status: Published

Journal: Acta Crystallographica Section F: Structural Biology Communications

Year: 2018

Volume: F74

Issue: 8

Pages: 496-505

Online publication date: 01/08/2018

Acceptance date: 03/05/2018

Date deposited: 20/08/2018

ISSN (electronic): 2053-230X

Publisher: International Union of Crystallography

URL: https://doi.org/10.1107/S2053230X18006842

DOI: 10.1107/S2053230X18006842


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