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Structural basis for the function of pyridoxine 5'-phosphate synthase.
1Max-Planck-Institut für Biochemie, Abteilung Strukturforschung, D-82152 Planegg-Martinsried, Germany.
Structure (London, England : 1993)
|April 5, 2001
Summary
The crystal structure of E. coli PNP synthase reveals its TIM barrel fold and active site dynamics. This provides insights into vitamin B(6) biosynthesis and enzyme mechanism.
Area of Science:
- Biochemistry
- Structural Biology
- Enzymology
Background:
- Vitamin B(6) (pyridoxal 5'-phosphate) is crucial for amino acid metabolism.
- Escherichia coli synthesizes vitamin B(6) de novo, producing pyridoxine 5'-phosphate (PNP) as the initial form.
- PNP synthase (PdxJ) catalyzes the final step in this biosynthesis pathway.
Purpose of the Study:
- To determine the high-resolution crystal structure of E. coli PNP synthase.
- To elucidate the enzyme's mechanism and active site architecture.
- To identify key amino acids involved in enzymatic function.
Main Methods:
- X-ray crystallography was used to solve the structure of PNP synthase.
- Single isomorphous replacement with anomalous scattering (SIRAS) was employed.
- Structures were refined at 2.0 Å and 2.3 Å resolution for the free enzyme and enzyme-product complex, respectively.
Main Results:
- The E. coli PNP synthase monomer features a TIM barrel fold.
- The enzyme forms a tetramer of symmetric dimers with 422 symmetry.
- Active sites revealed Arg20's role in substrate binding and identified critical amino acids in the enzyme-product complex.
Conclusions:
- The enzyme undergoes active site closure upon substrate binding.
- Key catalytic features include charge-charge stabilization of intermediates and dual phosphate binding sites.
- Related PNP synthases likely share a similar TIM barrel fold and catalytic mechanism.