CcpA and CodY Coordinate Acetate Metabolism in Streptococcus Mutans

In the dental caries pathogen , phosphotransacetylase (Pta) and acetate kinase (Ack) convert pyruvate into acetate with the concomitant generation of ATP. The genes for this pathway are tightly regulated by multiple environmental and intracellular inputs, but the basis for differential expression of the genes for Pta and Ack in had not been investigated. Here, we show that inactivation in of or reduced the activity of the promoter, whereas a mutant displayed elevated promoter activity. The interactions of CcpA with the promoter regions of both genes were observed using electrophoretic mobility shift and DNase protection assays. CodY bound to the promoter region but only in the presence of branched-chain amino acids (BCAAs). DNase footprinting revealed that the upstream region of both genes contains two catabolite-responsive elements ( and ) that can be bound by CcpA. Notably, the site of overlaps with a CodY-binding site. The CcpA- and CodY-binding sites in the promoter region of both genes were further defined by site-directed mutagenesis. Some differences between the reported consensus CodY binding site and the region protected by CodY were noted. Transcription of the and genes in the mutant strain was markedly different at low pH relative to transcription at neutral pH. Thus, CcpA and CodY are direct regulators of transcription of and in that optimize acetate metabolism in response to carbohydrate, amino acid availability, and environmental pH. The human dental caries pathogen is remarkably adept at coping with extended periods of carbohydrate limitation during fasting periods. The phosphotransacetylase-acetate kinase (Pta-Ack) pathway in modulates carbohydrate flux and fine-tunes the ability of the organisms to cope with stressors that are commonly encountered in the oral cavity. Here, we show that CcpA controls transcription of the and genes via direct interaction with the promoter regions of both genes and that branched-chain amino acids (BCAAs), particularly isoleucine, enhance the ability of CodY to bind to the promoter region of the gene. A working model is proposed to explain how regulation of and genes by these allosterically controlled regulatory proteins facilitates proper carbon flow and energy production, which are essential functions during infection and pathogenesis as carbohydrate and amino acid availability continually fluctuate.