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

Urresti, Saioa, Cartmell, Alan ORCID: 0000-0002-5512-249X, Liu, Feng, Walton, Paul H and Davies, Gideon J (2018) Structural studies of the unusual metal-ion site of the GH124 endoglucanase from Ruminiclostridium thermocellum. ACTA CRYSTALLOGRAPHICA SECTION F-STRUCTURAL BIOLOGY COMMUNICATIONS, 74 (Pt 8). pp. 496-505.

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Official URL: http://dx.doi.org/10.1107/s2053230x18006842

Abstract

The recent discovery of `lytic' polysaccharide monooxygenases, copper-dependent 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 Å) 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.

Item Type:	Article
Uncontrolled Keywords:	endoglucanase, Ruminiclostridium thermocellum, Clostridium, metal ion, oligosaccharides, enzymes, carbohydrates, bio-inorganic, 2-oxohistidine
Depositing User:	Symplectic Admin
Date Deposited:	10 Sep 2019 16:05
Last Modified:	05 Oct 2023 18:57
DOI:	10.1107/S2053230X18006842
Open Access URL:	https://www.ncbi.nlm.nih.gov/pmc/articles/PMC60964...
Related URLs:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3054139