Functional, structural, and taxonomical diversity of glycoside transporters in bacteria

Glycoside metabolization is a crucial function in bacteria and a key feature in fermentation and synthetic biology. To feed on various glycosides with complex structures, bacteria have developed very diverse mechanisms to recognize, transport, and degrade them. Despite their crucial role, transporters are hard to identify and study due to challenges in expressing membrane proteins in recombinant form and the fact that most bacteria are uncultivable. In this review, we present the available methods and technologies for identifying and characterizing bacterial glycoside transporters. We consolidate existing knowledge on experimentally validated glycoside transporters from different families, including TonB-dependent transporters, ATP-binding cassette transporters, the phosphotransferase system, and the major facilitator superfamily, highlighting their taxonomic, functional, mechanistic, and structural diversity. The disparity between the number of functionally characterized glycoside transporters and the vast amount of sequence data available underlines the need for more efficient approaches to determine their specificity and to better understand the molecular mechanisms of glycoside utilization in bacteria.