INFLUENCE OF HYDRATION ON THE INTERNAL DYNAMICS OF HEN EGG-WHITE LYSOZYME IN THE DRY STATE

Proteins exist in a predominately aqueous solvent environment. Hydrati on of the protein surface significantly affects many aspects of the pr otein's structure and function; these effects may be related to the mo lecular dynamics of the protein. We have examined the influence of hyd ration on the internal dynamics of hen egg white lysozyme using room-t emperature phosphorescence from the intrinsic tryptophan residues. Pow ders of lyophilized lysozyme were hydrated in a phosphorimeter using a flow system that allowed for continuous manipulation of relative humi dity over the range 0-92%; this system allowed us to directly compare intensity differences that result from changes in hydration. Lysozyme phosphorescence intensity decreased as a function of hydration over th e entire relative humidity range; the decrease was not linear but appe ared to occur in distinct phases. The phosphorescence intensity decays were multiexponential over the hydration range studied, and hydration had the largest influence on the long lifetime component. These data suggest that the protein exists in multiple, static conformations in t he dry state and that water binding to polar (as opposed to charged) s ites on the protein surface induces local and/or global softening of t he protein structure.