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

DOI: 10.1107/S2053230X18006842 DOI Help

Authors: Saioa Urresti (University of York) , Alan Cartmell (Newcastle University) , Feng Liu (University of British Columbia) , Paul H. Walton (University of York) , Gideon J. Davies (University of York)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Acta Crystallographica Section F Structural Biology Communications , VOL 74 , PAGES 496 - 505

State: Published (Approved)
Published: August 2018
Diamond Proposal Number(s): 13587

Open Access Open Access

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.

Journal Keywords: Ruminiclostridium thermocellum; Clostridium; metal ion; oligosaccharides; enzymes; carbohydrates; bio-inorganic; 2-oxohistidine

Diamond Keywords: Enzymes; Bacteria

Subject Areas: Biology and Bio-materials

Instruments: I02-Macromolecular Crystallography

Added On: 08/08/2018 09:24


Discipline Tags:

Structural biology Life Sciences & Biotech

Technical Tags:

Diffraction Macromolecular Crystallography (MX)