title: Protein crowding impedes pressure-induced unfolding of staphylococcal nuclease.
abstract: BACKGROUND
  In the cellular environment, macromolecules occupy about 30% of a cell's volume. In this crowded environment, proteins behave very differently than in dilute solution where scientists typically study the properties of proteins. For this reason, recent studies have investigated proteins in cell-like crowded conditions so as to understand if this changes their properties. The present study was performed to examine if molecular crowding impedes the protein unfolding process that is known to occur upon the application of high pressure.
  
  
  METHODS
  Crowding of staphylococcal nuclease (SNase) was induced by dissolving low concentrations of SNase in high concentrations of crowding agents (16 wt.% or 25 wt.% PEG 3000 or 16 wt.% Dextran T10). SNase unfolding was then monitored via tryptophan fluorescence as pressure was applied.
  
  
  RESULTS
  Fluorescence spectra can be decomposed into the sum of two components indicative, respectively, of native and unfolded states, and the center of spectral mass was then used as a measure of the degree of protein unfolding. It was found that SNase unfolding as a function of pressure was impeded in crowded solutions. These results suggest that crowded environments, such as those found in the cellular cytoplasm, may also impede high-pressure protein unfolding in cells.
  
  
  CONCLUSIONS
  This is the first report on the effect of crowding on the pressure-induced unfolding of a protein (staphylococcal nuclease) monitored via tryptophan fluorescence.
authors.affiliation: Laboratory of Atomic and Solid State Physics, Cornell High Energy Synchrotron Source, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Suntao
authors.initials: S
authors.lastname: Wang
authors.forename: Mark W
authors.initials: MW
authors.lastname: Tate
authors.forename: Sol M
authors.initials: SM
authors.lastname: Gruner
mesh_terms: D005453:Fluorescence; D007700:Kinetics; D008836:Micrococcal Nuclease / Q000737:chemistry* / Q000378:metabolism*; D011312:Pressure; D017510:Protein Folding; D055503:Protein Multimerization; D013816:Thermodynamics; D014364:Tryptophan / Q000737:chemistry
chemical_list: D014364:Tryptophan; D008836:Micrococcal Nuclease