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


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.

SUBMITTER: Urresti S 

PROVIDER: S-EPMC6096483 | biostudies-literature | 2018 Aug

REPOSITORIES: biostudies-literature

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

Urresti Saioa S   Cartmell Alan A   Liu Feng F   Walton Paul H PH   Davies Gideon J GJ  

Acta crystallographica. Section F, Structural biology communications 20180801 Pt 8


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 Ca<sup>2+</sup> site but features aspartic acid, asparagine and two histidine imidazoles as coordinating residues, which are m  ...[more]

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