Phosphorylation of serine‐46 in HPr, a key regulatory protein in bacteria, results in stabilization of its solution structure

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Abstract
The serine-phosphorylated form of histidine-containing protein (HPr), a component of the phosphoenol-pyruvate:sugar phosphotransferase system from Bacillus subtilis, has been characterized by NMR spectroscopy and solvent denaturation studies. The results indicate that phosphorylation of Ser 46, the N-cap of α-helix-B, does not cause a conformational change but rather stabilizes the helix. Amide proton exchange rates in helix-B are decreased and phosphorylation stabilizes the protein to solvent and thermal denaturation, with a ΔΔG of 0.7-0.8 kcal mol−1. A mutant in which Ser 46 is replaced by aspartic acid shows a similar stabilization, indicating that an electrostatic interaction between the negatively charged groups and the helix macrodipole contributes significantly to the stabilization.