Kinetics of dextran‐independent α‐(1→3)‐glucan synthesis by Streptococcus sobrinus glucosyltransferase I

Abstract

Glucosyltransferase (GTF)‐I from cariogenic Streptococcus sobrinus elongates the α‐(1→3)‐linked glucose polymer branches on the primer dextran bound to the C‐terminal glucan‐binding domain. We investigated the GTF‐I‐catalyzed glucan synthesis reaction in the absence of the primer dextran. The time course of saccharide production during dextran‐independent glucan synthesis from sucrose was analyzed. Fructose and glucose were first produced by the sucrose hydrolysis. Leucrose was subsequently produced, followed by insoluble glucan [α‐(1→3)‐linked glucose polymers] after a lag phase. High levels of intermediate nigerooligosaccharide series accumulation were characteristically not observed during the lag phase. The results from the enzymatic activity of the acceptor reaction for the nigerooligosaccharide with a degree of polymerization of 2–6 and methyl α‐d‐glucopyranoside as a glucose analog indicate that the activity increased with an increase in the degree of polymerization. The production of insoluble glucan was numerically simulated using the fourth‐order Runge–Kutta method with the kinetic parameters estimated from the enzyme assay. The simulated time course provided a profile similar to that of experimental data. These results define the relationship between the kinetic properties of GTF‐I and the time course of saccharide production. These results are discussed with respect to a mechanism that underlies efficient glucan synthesis.

In vitro synthesis of linear α-1,3-glucan and chemical modification to ester derivatives exhibiting outstanding thermal properties

“…1d . Thus, GtfJ works effectively in weak acidic region of pH and this phenomenon is similar to other different Gtfs from Streptococcus mutans 6715, Aureobasidium and Pseudomonas mesoacidophila MX-45 24 25 26 27 28 . Consequently, enzymatic reaction at pH 5.5 was performed throughout this research.…”

“…1 H-NMR spectra of α-1,3-glucan prepared from enzymatic polymerization with GtfJ enzyme were presented in past research papers but the elucidation of ring 1 H was not yet clearly shown and those α-1,3-glucan reported in related published papers contained branching α-1,6-linkage 9 25 . Herein, the HSQC spectrum as in Fig.…”

An α-1,6-and α-1,3-linked glucan produced by Leuconostoc citreum ABK-1 alternansucrase with nanoparticle and film-forming properties

“…Alternan produced by Lc ALT ( Lc -alternan) was subjected to NMR analysis to determine the pattern of glycosidic linkages. Lc -alternan could not be dissolved in 1 M NaOD, unlike other insoluble glucans 32 , 33 . Nevertheless, at high concentrations some Lc -alternan could be dissolved in D 2 O for NMR analysis.…”

Secreted expression of Leuconostoc mesenteroides glucansucrase in Lactococcus lactis for the production of insoluble glucans

“…Glucansucrases are often described based on amino acid alignments with other glucansucrase as having an Nterminal variable region, followed by a catalytic domain, and a C-terminal glucan-binding domain (Monchois et al 1999); however, structural analyses show that the protein actually contains five domains (A, B, C, IV, and V) that are formed through a U-shape configuration that involves two regions of the polypeptide for each domain, with the exception of domain C (Ito et al 2011;Meng et al 2015;Pijning et al 2014;Vujicic-Zagar et al 2010). Numerous studies have examined glucan-binding of the C-terminal repeat domain (Haas and Banas 2000;Kingston et al 2002;Monchois et al 1998;Shah et al 2004), which likely binds tightly to regions of α(1→6) in a strongly exothermic reaction (Komatsu et al 2011). We are currently studying the interactions between DsrI and soluble dextran in an attempt to further improve methods for purification of the enzyme.…”