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Bacterial phosphoenolpyruvate-dependent phosphotransferase system: P-Ser-HPr and its possible regulatory function?
J Deutscher1, U Kessler, C A Alpert
1Department of Microbiology, Ruhr-Universităt Bochum, NDEF 06, D-4630 Bochum, Federal Republic of Germany.
Biochemistry
|March 5, 2011
Summary
Phospho-Ser-HPr, a modified bacterial phosphotransferase system protein, is phosphorylated much slower than normal HPr. Its phosphorylation rate is significantly increased by specific factor III proteins, suggesting a regulatory role in sugar uptake.
Area of Science:
- Biochemistry
- Molecular Biology
- Microbiology
Background:
- The bacterial phosphotransferase system (PTS) utilizes histidine-containing protein (HPr) as a central phospho-carrier.
- HPr is typically phosphorylated on a histidyl residue by phosphoenolpyruvate (PEP) and enzyme I.
- A novel form, phospho-Ser-HPr, is generated via an ATP-dependent protein kinase.
Purpose of the Study:
- To investigate the substrate properties of phospho-Ser-HPr.
- To determine how phospho-Ser-HPr interacts with enzyme I and factor III proteins.
- To elucidate the regulatory mechanism of sugar uptake in the PTS.
Main Methods:
- Comparative phosphorylation assays using HPr and phospho-Ser-HPr.
- Enzymatic reactions involving PEP, enzyme I, and various factor III proteins.
- Kinetic analysis of phosphorylation rates.
Main Results:
- Phospho-Ser-HPr is phosphorylated approximately 5000 times slower by PEP and enzyme I compared to HPr.
- Factor III(Gct) significantly enhances phospho-Ser-HPr phosphorylation, restoring rates comparable to free HPr.
- Factor III(Lac) also enhances phosphorylation but to a lesser extent (70-100 fold slower than with Factor III(Gct)).
Conclusions:
- Phospho-Ser-HPr exhibits altered substrate kinetics compared to HPr.
- Interactions between phospho-Ser-HPr and factor III proteins modulate its phosphorylation by enzyme I.
- This interaction mechanism likely plays a role in regulating the preferential uptake of different PTS sugars.
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