The role of dynamic motions in proteins will be explored with respect to entropic contributions to the stability of a protein-protein complex involved in intracellular calcium signalling. 13C and/or 2H NMR spin relaxation will be employed to characterize the extent of dynamic motions throughout the structures of calcium-saturated calmodulin as well as in a high-affinity complex of calmodulin with the smMLCK peptide. The interface of this calmodulin-smMLCK complex is expected to resemble the protein-protein interface which maintains the integrity of the transduced calcium signal. Isotopic enrichment of the smMLCK peptide will be accomplished by overexpression as a fusion protein in E. coli, enabling the dynamics of both components of this complex interface to be mapped. The pressure sensitivity of these dynamic motions will be tested with the goal of estimating activated volumes associated with the dynamic motions. Efforts will be made to detect correlated motions and to find correlations between the extent of fluidlike motions and peptide- binding. If time allows,the sequence determinants of affinity and specificity of calmodulin complexes will be examined-in collaboration with other group members in the context of structure and dynamics.
