Outer membrane utilisomes mediate glycan uptake in gut Bacteroidetes.

Area of Science:

• Microbiology
• Structural Biology
• Human Microbiome Research

Background:

• Bacteroidetes are key human gut microbes that metabolize diverse glycans.
• SusCD protein complexes facilitate glycan uptake across the bacterial outer membrane.
• Interactions of outer membrane proteins in glycan acquisition are not well understood.

Purpose of the Study:

• To investigate the assembly and function of outer membrane protein complexes involved in glycan utilization in Bacteroides thetaiotaomicron.
• To elucidate the mechanism of glycan capture and transport by these bacterial systems.

Main Methods:

• Single-particle cryogenic electron microscopy (cryo-EM) was used to determine structures.
• Structures were obtained in both the absence and presence of glycan substrates.
• Biochemical and structural analyses were performed on levan and dextran utilization systems.

Main Results:

• Identified stable, multi-protein complexes termed "utilisomes" that assemble on SusCD transporters.
• Observed substrate-induced conformational changes within the utilisomes.
• Characterized the roles of individual components in substrate capture and processing.

Conclusions:

• Utilisomes represent functional glycan-utilizing machines in Bacteroidetes.
• Concerted conformational changes facilitate efficient glycan capture and transport.
• This work provides mechanistic insights into nutrient acquisition by the gut microbiota.