Multifunctional Nutrient-Binding Proteins Adapt Human Symbiotic Bacteria for Glycan Competition in the Gut by Separately Promoting Enhanced Sensing and Catalysis

Abstract

Our intestinal tract harbors trillions of symbiotic microbes. A critical function contributed by this microbial community is the ability to degrade most of the complex carbohydrates in our diet, which not only change from meal to meal but also cannot be digested by our own bodies. A numerically abundant group of gut bacteria called the Bacteroidetes plays a prominent role in carbohydrate digestion in humans and other animals. Currently, the mechanisms that allow this bacterial group to rapidly respond to available carbohydrates and then digest them efficiently are unclear. Here, we present novel functions for four carbohydrate-binding proteins present in one member of the Bacteroidetes, revealing that these proteins serve unique and separable roles in either initial nutrient sensing or subsequent digestion. Because the protein families investigated are numerous in other gut bacteria colonizing nearly all humans and animals, our findings are fundamentally important to understanding how symbiotic microbes assist human digestion.