Bonds broken and formed during the mixed-linkage glucan : xyloglucan endotransglucosylase reaction catalysed by Equisetum hetero-trans- β-glucanase.

Bonds broken and formed during the mixed-linkage glucan : xyloglucan endotransglucosylase reaction catalysed by Equisetum hetero-trans-β-glucanase.
Biochem J. 2017 Jan 20;:
Authors: Simmons TJ, Fry SC
Abstract
Mixed-linkage glucan : xyloglucan endotransglucosylase (MXE) is one of the three activities of the recently characterised hetero-trans-β-glucanase (HTG), which among land-plants is known only from Equisetum species. The biochemical details of the MXE reaction were incompletely understood - details that would promote understanding of MXE's role in vivo and enable its full technological exploitation. We investigated HTG's site of attack on one of its donor substrates, mixed-linkage (1→3),(1→4)-β-D-glucan (MLG), with radioactive oligosaccharides of xyloglucan as acceptor substrate. Comparing three different MLG preparations, we showed that the enzyme favours those with a high content of cellotetraose blocks. The reaction products were analysed by enzymic digestion, thin-layer chromatography, HPLC and gel-permeation chromatography. Equisetum HTG consistently cleaved the MLG at the third consecutive β-(1→4)-bond following (towards the reducing terminus) a β-(1→3)-bond. It then formed a β-(1→4)-bond between the MLG and the non-reducing terminal glucose residue of the xyloglucan oligosaccharide, consistent with its XTH subfamily membership. Using size-homogeneous barley MLG as donor substrate, we showed that HTG does n...

Source: The Biochemical Journal - January 19, 2017 Category: Biochemistry Authors: Simmons TJ, Fry SC Tags: Biochem J Source Type: research