A sweet new role for LCP enzymes in protein glycosylation

The peptidoglycan that surrounds Gram-positive bacteria is affixed with a range of macromolecules that enable the microbe to effectively interact with its environment. Distinct enzymes decorate the cell wall with proteins and glycopolymers. Sortase enzymes covalently attach proteins to the peptidoglycan, while LytR-CpsA-Psr (LCP) proteins are thought to attach teichoic acid polymers and capsular polysaccharides. Ton-That and colleagues have discovered a new glycosylation pathway in the oral bacterium Actinomyces oris in which sortase and LCP enzymes operate on the same protein substrate. The A. oris LCP protein has a novel function, acting on the cell surface to transfer glycan macromolecules to a protein, which is then attached to the cell wall by a sortase. The reactions are tightly coupled, as elimination of the sortase causes the lethal accumulation of glycosylated protein in the membrane. Since sortase enzymes are attractive drug targets, this novel finding may provide a convenient cell-based tool to discover inhibitors of this important enzyme family.