Chemoenzymatic Probes Reveal Peptidoglycan Recognition and Uptake Mechanisms in .

, the major fungal pathogen in humans, is under the strong influence of bacterial peptidoglycan fragments to undergo the yeast-to-hyphae transition, a key virulent step in pathogenesis and infections. However, due to the synthetic difficulties of obtaining peptidoglycan fragments for biological studies, mechanistic details of how recognizes and uptakes these peptidoglycan fragments have not been well elucidated. Notably, previous works have solely focused on the synthetic peptidoglycan ligand, muramyl dipeptide (MDP), despite its poor hyphal-inducing activity in . In this work, we isolated and purified natural peptidoglycan fragments via enzymatic degradation of bacteria cell wall sacculi and chemoenzymatically installed a series of functional d-amino acids into the natural muropeptide, creating peptidoglycan probes that bear photoaffinity, bio-orthogonal, or fluorescent functionality. Using these chemoenzymatic peptidoglycan probes, we established that natural peptidoglycan fragments, which are potent hyphal-inducers, interact with the Cyr1 sensor protein in the in-gel fluorescence assay as well as in pulldown studies. Moreover, we established that bacterial peptidoglycan probes enter cells via an energy-dependent endocytic process.