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Applied and Environmental Microbiology, September 2003, p. 5423-5432, Vol. 69, No. 9
0099-2240/03/$08.00+0 DOI: 10.1128/AEM.69.9.5423-5432.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Genetic and Biochemical Characterization of the Phosphoenolpyruvate:Glucose/Mannose Phosphotransferase System of Streptococcus thermophilus
Armelle Cochu, Christian Vadeboncoeur, Sylvain Moineau, and Michel Frenette*
Groupe de Recherche en Écologie Buccale, Faculté de Médecine Dentaire, and Département de Biochimie et de Microbiologie, Faculté des Sciences et de Génie, Université Laval, Québec, Québec G1K 7P4, Canada
Received 11 April 2003/
Accepted 29 June 2003
In most streptococci, glucose is transported by the phosphoenolpyruvate (PEP):glucose/mannose phosphotransferase system (PTS) via HPr and IIABMan, two proteins involved in regulatory mechanisms. While most strains of Streptococcus thermophilus do not or poorly metabolize glucose, compelling evidence suggests that S. thermophilus possesses the genes that encode the glucose/mannose general and specific PTS proteins. The purposes of this study were to determine (i) whether these PTS genes are expressed, (ii) whether the PTS proteins encoded by these genes are able to transfer a phosphate group from PEP to glucose/mannose PTS substrates, and (iii) whether these proteins catalyze sugar transport. The pts operon is made up of the genes encoding HPr (ptsH) and enzyme I (EI) (ptsI), which are transcribed into a 0.6-kb ptsH mRNA and a 2.3-kb ptsHI mRNA. The specific glucose/mannose PTS proteins, IIABMan, IICMan, IIDMan, and the ManO protein, are encoded by manL, manM, manN, and manO, respectively, which make up the man operon. The man operon is transcribed into a single 3.5-kb mRNA. To assess the phosphotransfer competence of these PTS proteins, in vitro PEP-dependent phosphorylation experiments were conducted with purified HPr, EI, and IIABMan as well as membrane fragments containing IICMan and IIDMan. These PTS components efficiently transferred a phosphate group from PEP to glucose, mannose, 2-deoxyglucose, and (to a lesser extent) fructose, which are common streptococcal glucose/mannose PTS substrates. Whole cells were unable to catalyze the uptake of mannose and 2-deoxyglucose, demonstrating the inability of the S. thermophilus PTS proteins to operate as a proficient transport system. This inability to transport mannose and 2-deoxyglucose may be due to a defective IIC domain. We propose that in S. thermophilus, the general and specific glucose/mannose PTS proteins are not involved in glucose transport but might have regulatory functions associated with the phosphotransfer properties of HPr and IIABMan.
* Groupe de Recherche en Écologie Buccale (GREB), Faculté de Médecine Dentaire, Université Laval, Québec, Québec G1K 7P4, Canada. Phone: (418) 656-2131, ext. 5502. Fax: (418) 656-2861. E-mail:
Michel.Frenette{at}greb.ulaval.ca.
Applied and Environmental Microbiology, September 2003, p. 5423-5432, Vol. 69, No. 9
0099-2240/03/$08.00+0 DOI: 10.1128/AEM.69.9.5423-5432.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
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