Human microsomal prostaglandin E synthase-1: purification, functional characterization, and projection structure...

Area of Science:

• Biochemistry
• Enzymology
• Molecular Biology

Background:

• Microsomal prostaglandin E synthase-1 (mPGES-1) is a key enzyme in prostaglandin synthesis.
• Understanding its enzymatic properties and structural organization is crucial for its role in biological pathways.

Purpose of the Study:

• To express, purify, and characterize human mPGES-1.
• To investigate its enzymatic activities, including prostaglandin synthesis and peroxidase functions.
• To determine its quaternary structure and evolutionary relationship to other enzymes.

Main Methods:

• Bacterial expression of histidine-tagged mPGES-1 in E. coli.
• Purification using hydroxyapatite and immobilized metal affinity chromatography.
• Enzymatic assays for PGH2 to PGE2 conversion, PGG2 to 15-hydroperoxy-PGE2 conversion, and peroxidase activity.
• Electron crystallography for structural determination and hydrodynamic studies for molecular weight and oligomeric state.

Main Results:

• Purified mPGES-1 demonstrated high catalytic efficiency (Vmax; 170 micromol min-1 mg-1, kcat/Km; 310 mm-1 s-1) for PGH2 to PGE2 conversion.
• The enzyme also catalyzed the formation of 15-hydroperoxy-PGE2 and exhibited peroxidase activity towards various hydroperoxides.
• Electron crystallography revealed a trimeric structure, similar to microsomal glutathione transferase 1, supported by hydrodynamic studies indicating a molecular weight of 215,000.

Conclusions:

• Human mPGES-1 is a catalytically active enzyme with significant prostaglandin E2 synthase activity.
• The enzyme possesses additional peroxidase and glutathione transferase activities, suggesting an evolutionary link to microsomal glutathione transferases.
• The trimeric organization of mPGES-1 is essential for its function and structural stability.