Optical Detection of Disordered Water in Protein Cavities Using Metalloporphyrins

Strategic Insights -

Metalloporphyrins have been at the center of a recent study investigating the detection of disordered water within protein cavities. Researchers from the University States have made a significant breakthrough in this area, utilizing subtle changes in the absorbance spectrum of pentacoordinate heme to detect water molecules within the distal cavities of myoglobin mutants. This innovative approach has far-reaching implications for our understanding of protein structure and function. The study highlights the importance of internal water molecules in maintaining protein stability and functionality, even in the absence of readily observable solvent in crystal structures.

Key Takeaways:

  • Researchers from the University of California discovered that internal water molecules play a crucial role in protein structure and function.
  • Disordered water within protein cavities can be detected using subtle changes in the absorbance spectrum of pentacoordinate heme.
  • The presence of a well-defined, noncoordinated water molecule in the distal heme pocket of wild-type deoxymyoglobin was observed in crystal structures.
  • Mutation of residues in myoglobin (L29F and V68L) resulted in the loss of discrete solvent positions in electron density maps, yet slow rates of ligand binding indicative of internal water were still observed.
  • Time-resolved perturbations of visible absorption bands after laser photolysis detected the entry and significant occupancy of water within the distal pockets of L29F and V68L deoxyMb variants.
  • The spectral perturbation of pentacoordinate heme offers a potentially robust system for measuring nonspecific hydration of the active sites of heme proteins.
  • R.A. Goldbeck and colleagues concluded that this approach could be applied to other heme proteins, providing new insights into protein function and stability.

Statistics:

  • The study focused on the myoglobin mutants L29F and V68L, which showed mutant rates of ligand entry indicative of internal water occupation.
  • The investigators detected the entry and significant occupancy of water within the distal pockets of these variants using time-resolved perturbations of visible absorption bands after laser photolysis.
  • The researchers published their findings in the Journal of the American Chemical Society (Optical detection of disordered water within a protein cavity. Journal of the American Chemical Society, 2009;131(34):12265-72).
  • The study's results have significant implications for understanding protein structure and function, particularly with respect to internal water molecules.

Sources:

  • Goldbeck, R. A., et al. "Optical detection of disordered water within a protein cavity." Journal of the American Chemical Society 131.34 (2009): 12265-72.
  • University of California, Dept. of Chemistry and Biochemistry, Santa Cruz, California 95064 USA.