Practical experience with the use of halides for phasing macromolecular structures: a powerful tool for structural...

Area of Science:

• Structural biology
• Protein crystallography
• Enzymology

Background:

• Pepstatin-insensitive carboxyl proteinase (PCP) from Pseudomonas sp. 101 exhibits no sequence similarity to other known proteinases.
• Determining the structure of novel enzymes is crucial for understanding their function and for drug discovery.

Purpose of the Study:

• To elucidate the three-dimensional crystal structure of PCP.
• To evaluate efficient methods for protein structure determination in structural genomics.

Main Methods:

• X-ray crystallography was employed using crystals soaked in sodium bromide and cryocooled.
• Single-wavelength anomalous diffraction (SAD) data collected at the bromine peak absorption wavelength.
• Comparison of SAD phasing with multiwavelength anomalous diffraction (MAD) phasing.

Main Results:

• An excellent electron density map was calculated from single-wavelength data, enabling structure solution with minimal human intervention.
• SAD phasing proved effective, comparable to the more labor-intensive MAD method for this enzyme.
• Bromine was validated as a suitable heavy-atom derivative for phasing.

Conclusions:

• Single-wavelength halide-based phasing is a highly effective and efficient method for high-throughput protein structure determination.
• This approach is well-suited for the demands of the emerging field of structural genomics.
• The crystal structure of PCP was successfully solved, providing insights into a novel class of proteinases.