Do Protein Molecules Unfold in a Simple Shear Flow?

• Published in: Biophysical journal 2006-11, Vol.91 (9), p.3415-3424
• Main Authors: Jaspe, Juan, Hagen, Stephen J.
• Format: Article
• Language: English
• Subjects: Animals; Biophysics; Computer Simulation; Cytochromes c - chemistry; Cytochromes c - ultrastructure; Fluorescence; Horses; Microfluidics - methods; Models, Chemical; Models, Molecular; Protein Conformation; Protein Denaturation; Protein Folding; Proteins; Shear Strength; Spectrum analysis; Stress, Mechanical; Temperature effects; Thermodynamics
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1529/biophysj.106.089367

Protein molecules typically unfold (denature) when subjected to extremes of heat, cold, pH, solvent composition, or mechanical stress. One might expect that shearing forces induced by a nonuniform fluid flow would also destabilize proteins, as when a protein solution flows rapidly through a narrow channel. However, although the protein literature contains many references to shear denaturation, we find little quantitative evidence for the phenomenon. We have investigated whether a high shear can destabilize a small globular protein to any measurable extent. We study a protein (horse cytochrome c, 104 amino acids) whose fluorescence increases sharply upon unfolding. By forcing the sample through a silica capillary (inner diameter 150–180 μm) at speeds approaching 10 m/s, we subject the protein to shear rates dv z /dr as large as ∼2 × 10 5 s −1 while illuminating it with an ultraviolet laser. We can readily detect fluorescence changes of