Comparative modeling studies of the calmodulin-like domain of calcium-dependent protein kinase from soybean
✍ Scribed by Aalim M. Weljie; Teresa E. Clarke; André H. Juffer; Alice C. Harmon; Hans J. Vogel
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 479 KB
- Volume
- 39
- Category
- Article
- ISSN
- 0887-3585
No coin nor oath required. For personal study only.
✦ Synopsis
Calmodulin-like domain protein kinases (CDPKs) represent a new class of calciumdependent protein-phosphorylating enzymes that are not activated by calmodulin or phospholipid compounds. They have been found exclusively in plant and protozoal tissues. CDPKs are typified by four distinct domains: an N-terminal leader sequence, a protein kinase (PK) domain, a calmodulinlike domain (CLD), and a junction domain (JD) between the PK domain and CLD. Structural characterization of the CLD of CDPK␣ from soybean was undertaken based on the amino acid sequence homology of CLD to the structurally well-characterized calmodulin (CaM) family of structures. Tertiary models of apo-CLD, Ca 2؉ -CLD complex, and intermolecularly bound Ca 2؉ -CLD-JD complexes were obtained via automated and non-automated homology building methods. The resulting structures were compared and validated based on energy differences, phi-psi angle distribution, solvent accessibility, and hydrophobic potential. Circular dichroism, one-dimensional, and two-dimensional nuclear magnetic resonance spectroscopy studies of the CLD and peptides encompassing the JD provide experimental support to the models. The results suggest that there is a possible interaction between the CLD and JD domain similar to that of the CaM/calmodulin-dependent protein kinase II system. At low Ca 2؉ levels, the JD may act as an autoinhibitory domain for kinase activity, and during calcium activation an intramolecular CLD-JD complex may form, relieving inhibition of the PK domain. Interactions between the JD and the C terminus of the CLD appear to be particularly important. The outcome of this study supports an intramolecular binding model for calcium activation of CDPK, although not exclusively.