Structural Determination of Glucosyltransferase C by Cryo-Electron Microscopy

Biofilm formation is a critical factor in the development of cariogenic virulence of Streptococcus mutans. S. mutans has evolved a concerted mechanism to synthesize a biofilm matrix from dietary sugars by a family of glucosyltransferases (Gtfs). Three Gtfs, GtfB, C, and D utilize sucrose to form a sticky polymer consisting of insoluble and soluble glucans, a biofilm foundation. Each Gtf possesses two distinct domains, an N-terminal enzyme catalytic domain and a C-terminal glucan binding domain. X-ray crystallographic studies have determined a three-dimensional structure of the catalytic domain of GtfC, however, the structure of the C-terminal domain and the overall structure of Gtfs are unknown. Here, we provided a protocol that will guide us to solve Gtf structures using cryo-electron microscopy (cryo-EM). Cryo-EM and X-ray crystallography are two widely used techniques for determining protein structures, and both methods have their own advantages and limitations. Additionally, we also predicted the full-length GtfC structural using AlphaFold2. Overall, the combination of AlphaFold 2 with experimental approaches offers a powerful and synergistic strategy for protein structure determination, accelerating the pace of scientific discovery and enabling new insights into the molecular basis that govern the biosynthetic activities of Gtfs, which may inform the design of more effective treatments for cariogenic biofilms and associated diseases.