Native SAD phasing at room temperature.

Area of Science:

• Structural biology
• Crystallography
• Biophysics

Background:

• Single-wavelength anomalous diffraction (SAD) is crucial for solving the phase problem in macromolecular crystallography.
• Cryogenic temperatures, typically used for SAD, can distort protein structures and hinder data merging.
• Radiation damage is a concern in X-ray crystallography, often necessitating low-temperature experiments.

Purpose of the Study:

• To develop and validate a strategy for high-quality SAD data collection at room temperature (295 K).
• To overcome limitations associated with cryogenic SAD experiments, such as altered protein conformations and non-uniform freezing.
• To demonstrate the feasibility of native SAD phasing at room temperature for structure determination.

Main Methods:

• Native SAD phasing was performed at 6.55 keV.
• Data were collected from single crystals at room temperature (295 K).
• Four structures from three model systems were solved using this room-temperature SAD approach.

Main Results:

• High-quality diffraction data were obtained at room temperature.
• Successful native SAD phasing enabled structure determination without cryoprotection.
• The method allowed for the observation of alternate protein conformations present at physiological temperatures.
• Automatic phasing and model building were facilitated by the collected data.

Conclusions:

• Room-temperature SAD is a viable strategy for accurate macromolecular structure determination.
• This method preserves native protein conformations, providing more biologically relevant structural information.
• The technique simplifies experimental procedures by eliminating the need for cryogenic conditions.