Structural analysis of the tetrahydrobiopterin glucosyltransferase <i>Ps</i> BGluT from <i>Pseudanabaena</i> sp. Chao 1811

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.