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

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. Copyright © 1995 The Protein Society