Modulation of the Surface-Layer Protein of Clostridium difficile through Cwp84 Inhibition.

Cysteine protease Cwp84 is responsible for surface-layer processing in Clostridium difficile and was also shown to cleave several human extracellular matrix components in vitro. To enable the facile identification and characterization of Cwp84 inhibitors, we developed a fluorogenic 10-mer peptide based on the enzyme's natural substrate SlpA that is amenable for use in FRET-based high-throughput screening. The design of substrate-mimetic inhibitors led to epoxysuccinate 8c, which displayed an inactivation efficiency (kinact/KI) of (4.7 ± 0.3) × 10(4) M(-1) min(-1). Further evaluation of 8c demonstrated its ability to inhibit fibronectin cleavage and, more importantly, subvert surface-layer biogenesis in C. difficile.