Bond Valence Sum Parameters for Analyzing Pyranopterin Tungsten Enzyme Structures

Area of Science:

• Biochemistry
• Structural Biology
• Crystallography

Background:

• X-ray crystallography of pyranopterin tungsten enzymes faces challenges.
• Fourier series termination and X-ray beam effects can impact data accuracy.

Purpose of the Study:

• Develop new bond valence sum (BVS) parameters for tungsten enzymes.
• Improve the determination of tungsten oxidation states and W-ligand bond lengths.
• Identify potential issues in existing pyranopterin tungsten enzyme crystal structures.

Main Methods:

• Derived new BVS parameters from X-ray crystallography data of W(+4) and W(+6) model compounds.
• Applied enzyme-specific BVS parameters to analyze pyranopterin tungsten enzyme structural data.
• Utilized Extended X-ray Absorption Fine Structure (EXAFS) for structural analysis.

Main Results:

• New BVS parameters revealed potential issues in enzyme crystal structures.
• Identified discrepancies in tungsten coordination, W-ligand bond lengths, and oxidation states.
• EXAFS data demonstrated higher accuracy for W-ligand bond distance determination.

Conclusions:

• BVS analysis of crystallographic and EXAFS data can resolve structural ambiguities.
• EXAFS should be routinely used for accurate active site structure determination in tungsten enzymes.
• Enhanced accuracy in W-ligand bond distance determination is crucial for understanding enzyme mechanisms.