Temperature-Dependent Interactions Explain Normal and Inverted Solubility in a γD-Crystallin Mutant

Area of Science:

• Biophysics
• Structural Biology
• Crystallography

Background:

• Protein crystallization is a critical bottleneck in determining protein structures.
• Predicting and optimizing crystallization requires understanding protein surface properties like chemical anisotropy.
• A gap exists between theoretical models of protein behavior and high-resolution structural data.

Purpose of the Study:

• To investigate the molecular basis of inverted solubility in a gammaD-crystallin mutant.
• To develop and apply a theoretical model linking protein phase diagrams to molecular details.
• To provide a rational strategy for protein crystallization.

Main Methods:

• Determined crystal structures of the P23T + R36S mutant of gammaD-crystallin.
• Utilized protein phase diagrams to analyze solubility behavior.
• Employed a tailored patchy particle model to simulate protein interactions.

Main Results:

• Two crystal structures with opposite temperature-dependent solubility were identified.
• A single, temperature-dependent interaction at the P23T site was found to stabilize the inverted solubility crystal.
• The P23T substitution was linked to genetic cataract and explained the protein's retrograde solubility.

Conclusions:

• The study demonstrates a molecular-level understanding of inverted protein solubility.
• The developed approach offers a productive strategy for rationalizing protein crystallization.
• This work bridges the gap between macroscopic phase behavior and microscopic interactions.