A complement to the modern crystallographer's toolbox: caged gadolinium complexes with versatile binding modes.

Area of Science:

• Biophysics
• Structural Biology
• Crystallography

Background:

• De novo phasing is crucial for determining protein structures.
• Introducing heavy atoms into protein crystals is a common method for phasing.
• Developing efficient heavy-atom vectors is essential for high-throughput structure determination.

Purpose of the Study:

• To develop and evaluate a set of novel gadolinium complexes as vectors for introducing heavy atoms into protein crystals.
• To assess the utility of these complexes for de novo phasing and structure determination.

Main Methods:

• Synthesis of seven caged gadolinium complexes with multidentate ligands.
• Crystallographic analysis of protein derivatives incorporating these complexes.
• Structure refinement to understand binding modes and interactions.

Main Results:

• Gadolinium complexes did not disrupt crystal diffraction quality.
• Up to 50% of derivatives yielded accurate phases, leading to high-quality electron-density maps.
• At least two successful derivatives were identified for all tested proteins, with versatile binding modes observed.

Conclusions:

• The gadolinium complexes are suitable heavy-atom screens for high-throughput de novo structure determination using Single-wavelength Anomalous Diffraction (SAD).
• These complexes can also be applied to emerging techniques like serial femtosecond crystallography.