Amino-terminal methionine processing of the protein HPr in Streptococcus salivarius grown in continuous culture

Authors

  • Christian Vadeboncoeur,

    Corresponding author
    1. Groupe de recherche en écologie buccale (GREB), Department of Biochemistry (Sciences) and Faculty of Dental Medicine, Université Laval, Québec, Canada
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  • Denis Brochu,

    1. Groupe de recherche en écologie buccale (GREB), Department of Biochemistry (Sciences) and Faculty of Dental Medicine, Université Laval, Québec, Canada
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  • Luc Trahan,

    1. Groupe de recherche en écologie buccale (GREB), Department of Biochemistry (Sciences) and Faculty of Dental Medicine, Université Laval, Québec, Canada
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  • Julie Fradette,

    1. Groupe de recherche en écologie buccale (GREB), Department of Biochemistry (Sciences) and Faculty of Dental Medicine, Université Laval, Québec, Canada
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  • Sébastien Gingras

    1. Groupe de recherche en écologie buccale (GREB), Department of Biochemistry (Sciences) and Faculty of Dental Medicine, Université Laval, Québec, Canada
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Correspondence to: Christian Vadeboncoeur, Groupe de recherche en écologie buccale (GREB), Department of Biochemistry (Sciences) and Faculty of Dental Medicine, Université Laval, Québec, Canada, G1K 7P4.

Abstract

Abstract HPr is a protein of the phosphoenolpyruvate:sugar phosphotransferase system (PTS). Streptococci possess two forms of HPr which differ by the presence or the absence of the N-terminal methionine (Met). These forms are called HPr-1 (without Met) and HPr-2 (with Met). In order to determine whether the ratio of these two forms varies with growth conditions, we measured the amount of HPr-1 and HPr-2 present in Streptococcus salivarius grown in continuous culture at pH 7.5. The results indicated that the HPr-1/HPr-2 ratio: 1) was not related to the cellular amount of total HPr; 2) was highest (10.2±3.5) under glucose (a PTS sugar) limitation (10 mM) and low dilution rate (D = 0.1 h−1; g = 6.9 h); 3) was decreased 2.4- to 5.7-fold when the amount of glucose and/or D was increased; 4) was not influenced by D when cells were cultured on galactose (a non-PTS sugar) but was two-fold higher under conditions of galactose excess (200 mM). We suggest that the cleavage of the N-terminal HPr Met is not a stochastic phenomenon but is dictated by growth conditions.

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