Calmodulin binding properties

K. P. Kohse and L. M. Heilmeyer, The effects of Mg2+ on the Ca2+-binding properties and Ca2 +-induced tyrosine-fluorescence changes of calmodulin isolated from rabbit skeletal muscle, Eur. J. Biochem. 117, 507-513 (1981). 

Recent investigations have shed light on peculiarities of the NOS action mechanism the role of the H4B cofactor and CaM, and cooperativity in kinetic and thermodynamic properties of different components of the nitric oxide synthesis system. Stop flow experiments with eNOS (Abu-Soud et al., 2000) showed that calmodulin binding caused an increase in NADH-dependent flavin reduction from 0.13 to 86 s 1 at 10 °C. Under such conditions, in the presence of Arg, heme is reduced very slowly (0.005 s 1). Heme complex formation requires a relatively high concentration ofNO (>50 nM) and inhibits the entire process NADH oxidation and citrulline synthesis decreases 3-fold and Km increases 3-fold. NOS reactions were monitored at subzero temperatures in the presence of 50% ethylene glycol as an anti-freeze solvent (Bee et al., 1998). 

This chapter will focus on the biochemical properties of MLCK in relation to its activation in smooth muscle and to recent insights into the molecular structure of the catalytic core and its regulation by an auto-inhibitory region and calmodulin binding domain. 

Figure 16.38- Schemade of the inteiactlona of the a-hetical MLCK peptide with calioodutin. The position of the single tryptophan residue is moved along the helix in 16 synthetic peptides. Reprinted, with permission. from O Neil, K. T., Wolfe, H. K, EricksM-Viitanen, S., and OeOrado, W. F. Fluorescence properties of calmodulin-binding peptides reflect alpha-helieal periodicity, Science 236 1454-1456, Copyright O 1987, American Association for the Advancemeat of Science.

Calcium effects. The biochemical effects of Ca "" in the cytoplasm are mediated by special Ca -binding proteins calcium sensors"). These include the annexins, calmodulin, and troponin C in muscle (see p. 334). Calmodulin is a relatively small protein (17 kDa) that occurs in all animal cells. Binding of four Ca "" ions (light blue) converts it into a regulatory element. Via a dramatic conformational change (cf 2a and 2b), Ca -calmodulin enters into interaction with other proteins and modulates their properties. Using this mechanism, Ca "" ions regulate the activity of enzymes, ion pumps, and components of the cytoskeleton. 

---