Do protein molecules unfold in a simple shear flow?

Biophys J. 2006 Nov 1;91(9):3415-24. doi: 10.1529/biophysj.106.089367. Epub 2006 Aug 4.


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 microm) at speeds approaching 10 m/s, we subject the protein to shear rates dv(z)/dr as large as approximately 2 x 10(5) s(-1) while illuminating it with an ultraviolet laser. We can readily detect fluorescence changes of <1%, corresponding to shifts of < approximately 0.01 kJ/mol in the stability of the folded state. We find no evidence that even our highest shear rates significantly destabilize the folded protein. A simple model suggests that extraordinary shear rates, approximately 10(7) s(-1), would be required to denature typical small, globular proteins in water.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Computer Simulation
  • Cytochromes c / chemistry*
  • Cytochromes c / ultrastructure*
  • Horses
  • Microfluidics / methods*
  • Models, Chemical*
  • Models, Molecular*
  • Protein Conformation
  • Protein Denaturation
  • Protein Folding
  • Shear Strength
  • Stress, Mechanical


  • Cytochromes c