Structural analysis of the tetrahydrobiopterin glucosyltransferase PsBGluT from Pseudanabaena sp. Chao 1811

Abstract

Pterin glycosides are widely distributed in cyanobacteria and have been implicated in the regulation of phototaxis and photosynthesis. Here, we identified a new uridine diphosphate glucose:tetrahydrobiopterin α-glucosyltransferase, termed PsBGluT, from Pseudanabaena sp. Chao 1811, which catalyzes the formation of pterin glycosides. We solved crystal structures of apo PsBGluT and its UDP-bound form at 2.8 and 2.3 Å resolution, respectively. PsBGluT forms a homodimer, with each subunit adopting a canonical GT-B fold composed of two Rossmann-like domains. Structural analysis combined with molecular docking revealed the binding sites for both the donor UDP-glucose and the acceptor tetrahydrobiopterin. Based on these findings, we proposed that PsBGluT operates via an S_Ni retaining catalytic mechanism. This study advances our understanding of pteridine glycosylation and also provides a structural basis for investigating the photosynthetic signaling pathways in cyanobacteria.