Calcium interactions with calmodulin

Calcium ion interactions with calmodulin, THERMODYNAMIC CYCLES Calcium oxalate,... 

Melittins are peptides of 26 amino acids found in Apis venoms (119, 120). Melittin comprises about 40% to 50% of the dry weight of Apis mellifera venom. At moderate and high concentrations, it exists primarily in the form of tetramers (120, 121), which can be immunogenic and allergenic (123). Tetrameric melittin is a potent lytic agent for cells and can also function as an ion channel (124, 125, 126). Melittin has profound effects on intracellular calcium and interacts with calmodulin (127, 128, 129). It is an amphiphilic and amphipathic molecule that has been found to be very useful in studies of cell lysis, membrane function, calcium regulation and as a model for proteins and peptides. Natural and synthetic melittin have been used in over a 1000 published studies in many areas of science. 

Fig. 10.3. Acceptor photobleaching analysis of interaction between barley MLO and calmodulin. Barley MLO is a plant-specific integral membrane protein that associates with the cytosolic calcium sensor protein Calmodulin...

Following these initial results, POWT was employed in the detection of protein conformational changes after a binding event. The protein used, calmodulin, is relatively small and functions as an intracellular calcium sensor in eukaryotic cells [26]. When calmodulin interacts with calcium, a large conformational change... 

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. 

Domain IV is the C-terminal portion of the protein, and is also known as the calmodulin-like domain due to its similarity with calmodulin. It contains five EF-hand Ca2+-binding motifs, the fifth of which does not bind calcium but is involved in the dimerization with the small subunit, through the interaction with the analogous EF-hand motif in domain VI. The small subunit is composed of two domains (V and VI) separated by a region containing a proline-rich stretch. 

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