Amino acid residues, calmodulin

Based on a sequence of 148 amino acid residues, calmodulin has a calculated molecular mass of 16,800, which lies about midway in a series of reported values determined by sedimentation... 

Hunter and Waltho have examined disulfide exchange in peptidic DCLs directed towards binding of the calcium transducer calmodulin (CaM) [23]. The DCL was based upon a known binding motif for CaM consisting of two hydrophobic peptides connected by a flexible linker—ideally suited to a DCC investigation. The library components are shown in Fig. 2.10, and consist of cystine dimers containing hydrophobic amino acid residues. 

Calmodulin from Tetrahymena presents interesting contrasts to calmodulins purified from vertebrate sources, and has, for example, 11 amino acid substitutions and one deletion of an amino acid residue compared to bovine brain calmodulin. Most of these variant residues are located near or at the III and IV Ca2+-binding sites. Tetrahymena calmodulin is very specific to... 

Positional scanning with phage libraries were used to discover the amino acid residues in peptides responsible for binding to the calciumbinding protein calmodulin.18 In this case, the binding polypeptide needed Trp as a key residue located in the fourteenth position from the N-terminus for strong binding. 

An offshoot of this protocol is the limited proteolysis strategy, in which proteolysis is restricted to a single event that cleaves the complex into two complementary fragments only this identifies the most susceptible bond in the protein and hence the protease-accessible amino acid residue. To identify other accessible residues, proteolysis is performed in a time-course fashion with a suite of enzymes of diverse specificities. The potential of the limited proteolysis strategy has been demonstrated by mapping the topology of Ca2+-calmodulin-melittin ternary complex.165... 

The 20-amino acid residue peptide RS-20, whose sequence derives from smooth muscle myosin light chain kinase (MLCK), is a well-known calmodulin binding peptide [144], Both, RS-20 and LMS-1, a 13-residue peptide derived from the autoinhibitory domain of MLCK, have the capability of inhibiting MLCK phosphorylation activity, normally directed toward the molecular motor, actin binding protein myosin II, which is involved in physiological phenomena like cell polarization and locomotion [145, 146]. 

Fig. 9.12. Calcium-calmodulin has four binding sites for calcium (shown in blue). Each calcium forms a multiligand coordination sphere by simultaneously binding several amino acid residues on calmodulin. Thus, it can create large conformational changes in proteins when it binds. Calmodulin has a flexible region in the middle connecting the two domains.

The low value of tensile force of CKA compared with those of poly-L-glutamic acid or poly-L-lysine was enigmatic at first. When they were compared with those of forced extension of calmodulin, it appeared to be due to partially helical polypeptide made of amino acid residues of small or moderate sized side chains. 

These methylated amino acid residues are present ubiquitously in nature, ranging from eukaryotic to prokaryotic organisms (1), and their presence are extremely selective occurring in highly spe-cialyzed proteins such as histone, flagella protein, myosin, actin, ribosomal proteins, opsin, fungal and plant cytochrome calmodulin and myelin basic protein. The methylation of these proteins... 

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