W0002

Conformational Flexibility in the Regulation of Target Proteins by Calmodulin and Troponin C. J. Trewhella, Joanna Krueger, Glenn Olah, Sue Rokop, Gang Zhi, and James Stull; Chemical Science and Technology Division, Mail Stop G758, Los Alamos National Laboratory, Los Alamos, NM 87545 USA

By combining solution scattering data with higher resolution information from NMR and crystallography, we have gained insights into the structure of calmodulin (CaM) and its interactions with target enzymes, as well as troponin C (TnC) and its interactions with troponin I. Our studies of CaM with the catalytically active skeletal muscle myosin light chain kinase (MLCK) provide direct structural evidence for the auto-inhibitory hypothesis of Ca²⁺/CaM kinase activation¹ and the effects of substrate binding on this interaction. The functionally diverse CaM and its more specialized cousin TnC are distinctive in their interactions, while sharing common structural motifs and mechanisms. They each show considerable conformational flexibility in their interactions, thus presenting special challenges to their study. Key to understanding their respective functions has been the ability to probe their structures and interactions with regulatory targets under a wide variety of conditions. To achieve this it has been important to be able to integrate structural data from a many different biophysical approaches. Small-angle X-ray and neutron scattering with contrast variation provide information on shapes of proteins and their dispositions in complexes and assemblies. When integrated with higher resolution NMR and crystallographic data, small-angle scattering data can provide the critical key to solving the jigsaw puzzle of how components fit together and are modulated by different signals.

¹Krueger J. K., Olah G. A., Rokop S. E., Zhi, G. Stull, J. T. and Trewhella, J. (1997) Biochemistry 36, 6017-6023.