Solvent Interaction Analysis: A New Lens for Protein Structure and Diagnostics

Area of Science:

• Biochemistry and Biophysics
• Analytical Chemistry
• Biomarker Discovery

Background:

• Aqueous two-phase systems (ATPSs) offer a unique, fully aqueous environment for studying solute-water interactions and protein structures.
• Phase behavior in ATPSs is governed by polymer chemistry and salt identity, which modulate water's solvent properties, influencing phase separation.
• Understanding these phase behaviors is crucial for developing novel analytical techniques in biochemistry.

Purpose of the Study:

• To review the principles and applications of ATPSs for probing solute-water interactions and protein structure.
• To highlight Solvent Interaction Analysis (SIA) as a method for generating protein structural signatures.
• To showcase SIA's utility in structure-based biomarker discovery and its clinical translation, exemplified by the IsoPSA assay.

Main Methods:

• Characterization of ATPS formation and composition using phase diagrams.
• Quantification of solvent properties (dipolarity, H-bonding, hydrophobicity, electrostatics) using solvatochromic probes and homologous solutes.
• Application of partition coefficients in various ATPSs to generate protein structural signatures via SIA, adaptable to vial, plate, and microfluidic formats.

Main Results:

• Phase separation and solute partitioning in ATPSs are predictable based on modulated solvent properties.
• SIA generates sensitive 'structural signatures' reflecting amino acid substitutions, conformational changes, ligand binding, and post-translational modifications, independent of protein size.
• The IsoPSA assay, utilizing SIA principles, successfully distinguishes high-grade prostate cancer from other conditions, demonstrating clinical utility.

Conclusions:

• Solvent Interaction Analysis (SIA) provides a mechanistically grounded, broadly applicable technology for protein characterization and drug-protein interaction studies.
• SIA is a powerful tool for structure-centric biomarker development, complementing conventional proteomic and glycomic approaches.
• The clinical success of the IsoPSA assay validates SIA's potential for disease diagnosis and risk stratification, particularly within the PSA 'gray zone'.