Flexibility of truncated and full‐length glucansucrase GTF 180 enzymes from Lactobacillus reuteri 180

Glucansucrase enzymes synthesize high‐molecular‐mass extracellular α‐glucan polysaccharides from sucrose. Previously, the crystal structure of truncated glucansucrase glucosyltransferase ( GTF )180‐ΔN from Lactobacillus reuteri 180 (lacking the N‐terminal domain) revealed an elongated overall structure with two remote domains ( IV and V) extending away from the core. By contrast, a new crystal form of the α‐1,6/α‐1,3 specific glucansucrase GTF 180‐ΔN shows an approximate 120 o rotation of domain V about a hinge located between domains IV and V, giving a much more compact structure than before. Positional variability of domain V in solution is confirmed by small angle X‐ray scattering experiments and rigid‐body ensemble calculations. In addition, small angle X‐ray scattering measurements of full‐length GTF 180 also provide the first structural data for a full‐length glucansucrase, showing that the enzyme has an almost symmetric boomerang‐like molecular shape, with a bend likely located between domains IV and V. The ~ 700‐residue N‐terminal domain, which is not present in the crystal structures, extends away from domain V and the catalytic core of the enzyme. We conclude that, as a result of the hinge region, in solution, GTF 180‐ΔN (and likely also the full‐length GTF 180) shows conformational flexibility; this may be a general feature of GH 70 glucansucrases. Database • Structural data for GTF180‐ΔN II have been deposited in the Protein Data Bank under accession code 4AYG .