COMPRESSIBILITY AS A MEANS TO DETECT AND CHARACTERIZE GLOBULAR PROTEIN STATES

We report compressibility data on single-domain, globular proteins whi ch suggest a general relationship between protein conformational trans itions and Delta k(S)(o), the change in the partial specific adiabatic compressibility which accompanies the transition. Specifically, we fi nd transitions between native and compact intermediate states to be ac companied by small increases in k(S)(o) of + (1-4) x 10(-6) cm(3) . g( -1). bar(-1) (1 bar = 100 kPa). By contrast, transitions between nativ e and partially unfolded states are accompanied by small decreases in k(S)(o) of -(3-7) x 10(-6) cm(3) . g(-1). bar(-1), while native-to-ful ly unfolded transitions result in large decreases in k(S)(o) of -(18-2 0) x 10(-6) cm(3) . g(-1). bar(-1). Thus, for the single-domain, globu lar proteins studied here, changes in k(S)(o) correlate with the type of transition being monitored, independent of the specific protein. Co nsequently, k(S)(o) measurements may provide a convenient approach for detecting the existence of and for defining the nature of protein tra nsitions, while also characterizing the hydration properties of indivi dual protein states.