Phosphoglycerate mutase is a highly efficient enzyme without flux control in Lactococcus lactis

Area of Science:

• Biochemistry
• Enzymology
• Microbial Metabolism

Background:

• Phosphoglycerate mutase (PGM) is a key glycolytic enzyme.
• Understanding PGM's role in Lactococcus lactis is crucial for metabolic studies.

Purpose of the Study:

• To investigate the function, kinetics, and glycolytic flux control of PGM in Lactococcus lactis.
• To characterize PGM activity across a range of expression levels.

Main Methods:

• Constructed a library of L. lactis strains with varying PGM activities using synthetic promoters.
• Measured specific growth rate, glucose flux, and mixed acid fluxes.
• Determined kinetic parameters (Km, kcat) and cofactor dependency.

Main Results:

• Specific growth rate and glucose flux were maximal at wild-type PGM levels, where PGM showed no flux control.
• Reduced PGM activity (15% of wild-type) led to a six-fold increase in catalytic rate.
• PGM demonstrated high catalytic efficiency (Km = 1.0 mM, kcat = 3,200 s⁻¹) and required 2,3-bisphosphoglyceric acid, indicating it's a dPGM type.

Conclusions:

• L. lactis PGM is a highly efficient catalyst.
• The enzyme's efficiency explains its limited flux control in wild-type L. lactis.
• PGM activity is a critical factor in regulating glycolytic flux.