1. MOLECULAR RESPONSE OF CHICKEN EGG WHITE LYSOZYME TO
BUFFER SALT CONCENTRATIONS AND pH
John P Sumida1, Natalie Kirkland2, Marc Pusey3; 1Universities Space Research
Association, 4950 Corporate Drive, Suite 100, Huntsville, Alabama 35805, 2University of
Alabama, Huntsville, 3NASA/Marshall Space Flight Center
Chicken egg white lysozyme, (CEWL), has been widely used as a model for the study of
protein crystal growth. Protein crystal growth bears direct relevance to drug design and
development in that the ability to produce better quality protein crystals results in more
accurate structure determinations. Having more accurately defined drug targets results in
more effective drug design. In order to produce high quality protein crystals, an
understanding of the mechanisms involved in protein crystal growth is essential.
The present study examines role of the solvent in protein nucleation, and specifically, the
dependence of the rotational dynamics of CEWL on the salt concentration and pH. Using
time resolved fluorescence anisotropy of fluorescently labelled lysozyme, the rotational
lifetime is observed to increase to a maximum at specific salt concentrations. Increasing
the pH, acts to shift the observed rotational maximum to a higher salt concentration.
Also observed in this work is evidence suggestive of energy transfer between the
fluorophore and Trp 63. The magnitude of the energy transfer also changes with both salt
concentration and pH in a manner similar to the anisotropy changes. These observations
suggest small changes in the protein conformation and hydrodynamic volume in response
to the solvent environment.