6g1g

Publication Abstract from PubMed

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(2+) 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 (Fe(2+), Cu(2+), Mn(2+) and Ni(2+)), 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.

Structural studies of the unusual metal-ion site of the GH124 endoglucanase from Ruminiclostridium thermocellum.,Urresti S, Cartmell A, Liu F, Walton PH, Davies GJ Acta Crystallogr F Struct Biol Commun. 2018 Aug 1;74(Pt 8):496-505. doi:, 10.1107/S2053230X18006842. Epub 2018 Aug 1. PMID:30084399^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.