The Structural Determinations of the Leucine Zipper Coiled-Coil Domains of the cGMP-Dependent Protein Kinase Iα and Its Interaction with the Myosin Binding Subunit of the Myosin Light Chains Phosphase

Physiologic relaxation of vascular smooth muscle is induced by the cyclic guanosine monophosphate (cGMP)dependent protein kinase I enzyme (cGKI alpha), which activates myosin phosphatase (MLCP). This activation process is thought to occur through the interaction involving both N- and C-terminal leucine zipper coiled-coil (LZCC) domains of the kinase enzyme (cGKI alpha) with the myosin binding subunit (MBS) of MLCP. In this review, I summarize how to define the LZCC domains in both N-terminal cGKI alpha(1-59) and C-terminal MBS proteins using predictive and experimental methods, how to make a rapid and accurate structure determination of a cGKI alpha(1-59) molecule using NMR's residual dipolar coupling (RDC) measurements, and how to indentify the existence of a weak protein interaction between N-terminal LZCC domain (cGKI alpha(1-59)) and a LZCC domain (MBSCT42) within the C-terminal MBS. In addition, the location and orientation of the residues in LZCC proteins can be readily visualized using a novel diagram, the so-called wenxiang diagram, which is more advantageous than traditional helical wheel diagrams in analyzing LZCC protein structures and their action mechanisms. Using the composed wenxiang diagrams, we have characterized the interaction between cGKI alpha(1-59) and another LZCC molecule (MBSCT42), and deduced that the most affected residues of these two LZCC molecules might be at the positions d, a, e and g. These studies and findings are also covered in this review. It is intriguing to see that the successful incorporation of wenxiang diagrams and NMR spectroscopy in the LZCC structural and functional studies may provide some insights into protein-protein interaction mechanisms.