6-Phosphogluconolactonase is critical for the efficient functioning of the pentose phosphate pathway

Area of Science:

• Microbiology
• Metabolic Engineering
• Biochemistry

Background:

• Microbial metabolic networks exhibit remarkable robustness due to redundancies like gene duplications and alternative pathways.
• The oxidative branch of the pentose phosphate pathway (oxPPP) relies on 6-phosphogluconolactonase (Pgl) for 6-phosphogluconolactone hydrolysis.
• In Pgl's absence, spontaneous hydrolysis and potential extracellular pathways are hypothesized to maintain oxPPP flux.

Purpose of the Study:

• To investigate whether intracellular non-enzymatic reactions can compensate for the absence of Pgl in Escherichia coli.
• To determine the role of Pgl in maintaining the flux of the oxPPP and its impact on central metabolism.
• To elucidate the contribution of extracellular pathways to pentose phosphate synthesis in Δpgl mutants.

Main Methods:

• Genetic manipulation of Escherichia coli to create Δpgl mutants.
• Metabolic flux analysis to quantify pathway contributions.
• Characterization of extracellular hydrolysis pathways for gluconolactones.

Main Results:

• The study validates an active bypass pathway in Δpgl Escherichia coli, involving extracellular spontaneous hydrolysis of gluconolactones.
• Metabolic flux analysis confirmed this bypass pathway accounts for the entire oxPPP flux in the absence of Pgl.
• Cell growth is sustained via this alternative, partially extracellular route, but at a reduced rate compared to wild-type.

Conclusions:

• Intracellular non-enzymatic hydrolysis of 6-phosphogluconolactone does not compensate for the absence of Pgl.
• An extracellular pathway sustains oxPPP flux in Pgl-deficient E. coli, highlighting metabolic flexibility.
• Pgl plays a crucial role in ensuring the efficient functioning of the oxPPP for optimal cellular metabolism.