CovR and VicRKX Regulate Transcription of the Collagen Binding Protein Cnm of Streptococcus mutans.

Cnm is a surface-associated protein present in a subset of strains that mediates binding to extracellular matrices, intracellular invasion, and virulence. Here, we showed that transcription is controlled by the global regulators CovR and VicRKX. analysis identified multiple putative CovR- and VicR-binding motifs in the regulatory region of as well as in the downstream gene , which is associated with the posttranslational modification of Cnm. Electrophoretic mobility shift assays revealed that CovR and VicR specifically and independently bind to the and promoter regions. Quantitative real-time PCR and Western blot analyses of Δ and Δ strains as well as of a strain overexpressing revealed that CovR functions as a positive regulator of , whereas VicRKX acts as a negative regulator. In agreement with the role of VicRKX as a repressor, the Δ strain showed enhanced binding to collagen and laminin and higher intracellular invasion rates. Overexpression of was associated with decreased rates of intracellular invasion but did not affect collagen or lamin binding activities, suggesting that this system controls additional genes involved in binding to these extracellular matrix proteins. As expected, based on the role of CovR in regulation, the Δ strain showed decreased intracellular invasion rates, but, unexpectedly collagen and laminin binding activities were increased in this mutant strain. Collectively, the results presented here expand the repertoire of virulence-related genes regulated by CovR and VicRKX to include the core gene and the noncore gene is a major pathogen associated with dental caries and also implicated in systemic infections, in particular, infective endocarditis. The Cnm adhesin of is an important virulence factor associated with systemic infections and caries severity. Despite its role in virulence, the regulatory mechanisms governing expression are poorly understood. Here, we describe the identification of two independent regulatory systems controlling the transcription of and the downstream operon. A better understanding of the mechanisms controlling expression of virulence factors like Cnm can facilitate the development of new strategies to treat bacterial infections.