Calcium binding fold

The location of the bound calcium(II) ion was unequivocally identified (see Fig. 8). Tbis is probably the most important feature of this work anfurther discussed in Sections VI and VII (see also Table IX). It should be emphasized here that the calcium-binding fold in a-lactalbumin resembles only superficially the EF-hand of those calcium-binding proteins that exhibit this feature (Fried-berg, 1988 see also Stuart et al., 1986). 

Calcium binding fold this is a pattern of two p-strands and three a-hefices that represents part of a calcium-binding domain found within the muscle protein Troponin-C (Protein Data Bank code 2TNC). 

Once the similarities for the output from the initial search have been calculated, the structures can be displayed via FRODO for visual inspection and evaluation of the rankings. The effectiveness of the algorithm was tested using the three motifs described above i.e., the eight-stranded P-barrel, the NAD-binding fold and the calcium-binding fold. 

In summary, the ranking was successful in that the known calcium-binding folds of troponin-C, calcium-binding parvalbumin B and calmodulin were contained within the top six ranking positions. An inspection of the distance distributions for these six structures reveals a substantial degree of similarity with the distribution for the query motif, and similar comments apply to the ICLN hits ranked seventh and eighth. After this, however, the distributions become markedly dissimilar. 

The efficiencies of the parallel and serial versions of the similarity algorithm have been investigated using the three query motifs (calcium binding fold, -barrel and NAD binding fold) discussed in the paper by Artymiuk et The serial... 

Parameters Calcium binding fold / -barrel NAD binding fold ... 

Structure of the first C2 domain of synaptotagmin I a novel calcium/phosphohpid-binding fold. Cell 80 929-938. 

The proximal calcium binding site is coupled to the heme group by virtue of the fact that one of its ligands, Thrl71, is adjacent to the proximal histidine residue, Hisl70 (Fig. 4). The results of site-directed mutagenesis studies at this position are awaited with interest. An illustration of the importance of both calcium sites to the structure and function of HRP C is afforded by the need to incorporate calcium as a component of in vitro folding mixtures to obtain active recombinant enzyme from solubilized inclusion bodies (64). 

Knhlman, B., J.A. Boice, W.J. Wn, R. Fairman, and D.P. Raleigh, Calcium binding peptides from alpha-lactalbumin implications for protein folding and stability. Biochemistry, 1997.36(15) 4607-15. 

We now consider two calcium binding proteins, parvalbumin and troponin. The first, carp parvalbumin, is a small protein of known crystal structure.41 It binds two Ca2+ ions per molecule. One of the Ca2+ ions is essential for a folded structure to be maintained the second may be lost with a relatively small conformational change.42... 

The situation in the calcium-binding protein aequorin is that there is a store of energy built into a special organic molecule and into the fold of the protein. On binding calcium the protein emits lights at around 500 nm and there is a conformational change of the protein. It is not easy to write... 

In conclusion, troponin binds Ca2+ in six-fold coordination and all oxygen ligands are provided from amino acids. No water is needed for the coordination complex. Aspartic acid and glutamic acid occupy key positions in the four calcium binding regions of the molecule. Transfer of calcium to tropomyosin and the actin filament during contraction is achieved by coordination changes. 

The subtilisins are a large family of serine proteases that have been extensively studied because of their importance in the detergent industry. The retain a common conserved fold and identical active site residues (Fig. 10). Two conserved calcium-binding sites are present in all subtilisins, and additional sites may be present in subtilisins from different organisms (Siezen and Leunissen, 1997). 

The main function of the intracellular calcium binding proteins is to modulate cellular events in response to the calcium signal. Analysis of the sequence of many of the intracellular calcium binding proteins has suggested the existence of two distinct families the EF domain family and the annexin fold family. For completeness, we have grouped the remainder of the intracellular calcium binding proteins into a miscellaneous category. 

When proteins fold into their tertiary structures, there are often subdivisions within the protein, designated as domains, which are characterised by similar features or motifs. A protein domain is a part of the protein sequence and structure that can evolve, function and exist independently of the rest of the protein chain. Many proteins consist of several structural domains. One domain may appear in a variety of evolutionarily related proteins. Domains vary in length from about 25 up to 500 amino acids. The shortest domains, such as zinc fingers , are stabilised by metal ions or disulfide bridges. Domains often form functional units, such as the calcium-binding EF hand domain of calmodulin. As they are self-stable, domains can be swapped by genetic engineering between one protein and another, to make chimera proteins. 

Inositol trisphosphate opens a calcium transport channel in the membrane of the endoplasmic reticulum. This leads to an influx of calcium from storage in the endoplasmic reticulum and a 10-fold increase in the cytosolic concentration of calcium ions. Calmodulin is a small calcium binding protein found in all cells. Its affinity for calcium is such that, at the resting concentration of calcium in the cytosol (of the order of 0.1 /xmol per L), little or none is bound to calmodulin. When the cytosolic concentration of calcium rises to about 1 /xmol per L, as occurs in response to opening of the endoplasmic reticulum calcium transport channel, calmodulin binds 4 mol of calcium per mol of protein. When this occurs, calmodulin undergoes a conformational change, and calcium-calmodulin binds to, and activates, cytosolic protein kinases, which in turn phosphorylate target enzymes. 

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