title: Genetic analysis of the functions and interactions of components of the LevQRST signal transduction complex of Streptococcus mutans.
abstract: Transcription of the genes for a fructan hydrolase (fruA) and a fructose/mannose sugar:phosphotransferase permease (levDEFG) in Streptococcus mutans is activated by a four-component regulatory system consisting of a histidine kinase (LevS), a response regulator (LevR) and two carbohydrate-binding proteins (LevQT). The expression of the fruA and levD operons was at baseline in a levQ mutant and substantially decreased in a levT null mutant, with lower expression with the cognate inducers fructose or mannose, but slightly higher expression in glucose or galactose. A strain expressing levQ with two point mutations (E170A/F292S) did not require inducers to activate gene expression and displayed altered levD expression when growing on various carbohydrates, including cellobiose. Linker-scanning (LS) mutagenesis was used to generate three libraries of mutants of levQ, levS and levT that displayed various levels of altered substrate specificity and of fruA/levD gene expression. The data support that LevQ and LevT are intimately involved in the sensing of carbohydrate signals, and that LevQ appears to be required for the integrity of the signal transduction complex, apparently by interacting with the sensor kinase LevS.
authors.affiliation: Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, Florida, United States of America. lzeng@dental.ufl.edu
authors.forename: Lin
authors.initials: L
authors.lastname: Zeng
authors.forename: Satarupa
authors.initials: S
authors.lastname: Das
authors.forename: Robert A
authors.initials: RA
authors.lastname: Burne
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D004843:Epistasis, Genetic / Q000235:genetics / Q000502:physiology; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D053263:Gene Regulatory Networks; D005947:Glucose / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D000071677:Histidine Kinase; D008358:Mannose / Q000378:metabolism; D009876:Operon / Q000235:genetics / Q000502:physiology; D030781:Organisms, Genetically Modified; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D015398:Signal Transduction / Q000235:genetics* / Q000502:physiology; D013295:Streptococcus mutans / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; D011956:Receptors, Cell Surface; D014157:Transcription Factors; C055213:saccharide-binding proteins; D011494:Protein Kinases; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System; D000071677:Histidine Kinase; D006026:Glycoside Hydrolases; C021512:levanase; D005947:Glucose; D008358:Mannose