Calcium binding

One calcium-binding motif found in proteins is the helixloophelix motif, also known as an EF hand [74, 75]. A comparison, diagrammed in Fig. 29, is made 

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The amount of each element required in daily dietary intake varies with the individual bioavailabihty of the mineral nutrient. BioavailabiUty depends both on body need as deterrnined by absorption and excretion patterns of the element and by general solubiUty, and on the absence of substances that may cause formation of iasoluble products, eg, calcium phosphate, Ca2(P0 2- some cases, additional requirements exist either for transport of substances or for uptake or binding. For example, calcium-binding proteias are iavolved ia calcium transport an intrinsic factor is needed for vitamin cobalt,... 

Fig. 2. Homeostatic control of blood Ca " level where PTH is parathyroid hormone [9002-64-6], CC, cholecalciferol, ie, vitamin D HCC, hydroxycholecalciferol DHCC, dihydroxycholecalciferol CaBP, calcium-binding protein NAD PH, protonated nicotinarnide-adenine dinucleotide...

Calcium is absorbed from the intestine by facilitated diffusion and active transport. In the former, Ca " moves from the mucosal to the serosal compartments along a concentration gradient. The active transport system requires a cation pump. In both processes, a calcium-binding protein (CaBP) is thought to be required for the transport. Synthesis of CaBP is activated by 1,25-DHCC. In the active transport, release of Ca " from the mucosal cell into... 

Calcium-binding protein is not found in the intestinal mucosa of vitamin D-deficient animals. It is synthesized only in response to the presence of a material with vitamin D activity. Thus, using antisemm specific to intestinal calcium-binding protein, a radioimmunodiffusion assay (98) conducted on ... 

One of these motifs, called the helix-turn-helix motif, is specific for DNA binding and is described in detail in Chapters 8 and 9. The second motif is specific for calcium binding and is present in parvalbumin, calmodulin, tro-ponin-C, and other proteins that bind calcium and thereby regulate cellular activities. This calcium-binding motif was first found in 1973 by Robert Kretsinger, University of Virginia, when he determined the structure of parvalbumin to 1.8 A resolution. 

Parvalbumin is a muscle protein with a single polypeptide chain of 109 amino acids. Its function is uncertain, but calcium binding to this protein probably plays a role in muscle relaxation. The helix-loop-helix motif appears three times in this structure, in two of the cases there is a calcium-binding site. Figure 2.13 shows this motif which is called an EF hand because the fifth and sixth helices from the amino terminus in the structure of parvalbumin, which were labeled E and F, are the parts of the structure that were originally used to illustrate calcium binding by this motif. Despite this trivial origin, the name has remained in the literature. 

Figure 2.12 Two a helices that are connected by a short loop region in a specific geometric arrangement constitute a helix-turn-helix motif. Two such motifs are shown the DNA-binding motif (a), which is further discussed in Chapter 8, and the calcium-binding motif (b), which is present in many proteins whose function is regulated by calcium.

Table 2.2 Amino acid sequences of calcium-binding EF motifs in three different proteins Pamalbumin VKKAFAI I DQDKSGFIEEDELKLFLQNF Calmodulin FKEAFSLFDKDGDGT I TTKELGTVMRSL Troponin-C LADCFR I FDKNADGF I D lEELGE I LRAT...

Calcium-binding residues are brown, and residues that form the hydrophobic core of the motif are light green. The helix-loop-helix region shown underneath is colored as in Figure 2.13. 

Figure 2.19 Organization of polypeptide chains into domains. Small protein molecules like the epidermal growth factor, EGF, comprise only one domain. Others, like the serine proteinase chymotrypsin, are arranged in two domains that are required to form a functional unit (see Chapter 11). Many of the proteins that are involved in blood coagulation and fibrinolysis, such as urokinase, factor IX, and plasminogen, have long polypeptide chains that comprise different combinations of domains homologous to EGF and serine proteinases and, in addition, calcium-binding domains and Kringle domains.

Moews, P.C., Kretsinger, R.H. Refinement of the structure of carp muscle calcium-binding parvalbumin by model building and difference Fourier analysis. 

Boumann, U., et al. Three-dimensional structure of the alkaline protease of Pseudomonas aeruginosa, a two-domain protein with a calcium binding parallel beta roll motif. EMBO J. 12 3357-3364, 1993. 

Nonrepetitive but well-defined structures of this type form many important features of enzyme active sites. In some cases, a particular arrangement of coil structure providing a specific type of functional site recurs in several functionally related proteins. The peptide loop that binds iron-sulfur clusters in both ferredoxin and high potential iron protein is one example. Another is the central loop portion of the E—F hand structure that binds a calcium ion in several calcium-binding proteins, including calmodulin, carp parvalbumin, troponin C, and the intestinal calcium-binding protein. This loop, shown in Figure 6.26, connects two short a-helices. The calcium ion nestles into the pocket formed by this structure. 

C, which is found in complement proteins FI, F2, and F3, first found in fibronectin I, the immunoglobulin superfamily domain N, found in some growth factor receptors E, a module homologous to the calcium-binding E-F hand domain and LB, a lectin module found in some cell surface proteins. (Adapted from Baron, M., Norman, D., and Campbell, I., 1991, Protein modnles. Trends in Biochemical Sciences 16 13—1 7.)... 

Two types of stabilized coelenterazine are known to exist in biolu-minescent organisms, i.e. the protein-bound form (usually bound to a calcium-binding protein) and the enol ester form (usually enol-sulfate see Structure I, Fig. 5.5). 

Cormier, M. J., and Charbonneau, H. (1977). Isolation, properties and function of a calcium-triggered luciferin binding protein. In Wasserman, R. H., et al. (eds.), Calcium Binding Proteins and Calcium Function, pp. 481-489. Elsevier North-Holland. 

Illarionova, V. A., et al. (1997). Removal of essential ligand in N-terminal calcium-binding domain of obelin does not inactivate the photoprotein or reduce its calcium sensitivity, but dramatically alters the kinetics of the luminescent reaction. In Hastings, J. W., et al. (eds.), Biolu-min. Chemilumin., Proc. Int. Symp., 9th, 1996, pp. 431 —434. Wiley, Chichester, UK. 

Inouye, S., et al. (1989). Overexpression and purification of the recombinant calcium-binding protein, apoaequorin./. Biochem. 105 473-477. 

Kurose, K., Inouye, S., Sakaki, Y., and Tsuji, F. I. (1989). Bioluminescence of the calcium-binding photoprotein aequorin after cysteine modification. Proc. Natl. Acad. Sci. USA 86 80-84. 

Nagano, K., and Tsuji, F. I. (1990). Dimeric interaction of calcium-binding photoprotein aequorin. In Rivier, J. E., and Marshall, G. R. (eds.), Pept. Chem., Struct. Biol., Proc. Am. Pept. Symp., 11th, 1989, pp. 508-509. ESCOM Sci. Pub., Leiden, Netherland. 

Ohmiya, Y., and Hirano, T. (1996). Shining the light the mechanism of the bioluminescence reaction of calcium-binding photoproteins. Chem. Biol. 3 337-347. 

Prasher, D., McCann, R. O., and Cormier, M. J. (1985). Cloning and expression of the cDNA coding for aequorin, a bioluminescent calcium-binding protein. Biochem. Biophys. Res. Commun. 126 1259-1268. 

Sakaki, Y., et al. (1988). Structure and function of the calcium-binding photoprotein aequorin studies by recombinant DNA technology. In Yagi, Y., and Miyazaki, T. (eds.), Calcium Signal Cell Response, pp. 151-156. Jpn. Sci. Soc. Press Tokyo, Japan. 

Shimomura, O., and Johnson, F. H. (1970b). Calcium binding, quantum yield, and emitting molecule in aequorin bioluminescence. Nature 227 1356-1357. 

CAPL (S100A4) Calcium-binding protein Decrease of in vitro invasion reduction in expression of MMP-2, MT1-MMP, and TIM P-1 decrease of in vivo metastatic ability... 

These calcium-binding proteins form a superfamily of proteins containing more than 600 members [1-3]. The... 

These cytosolic proteins contain five EF-hand domains and are able to translocate to the plasma membrane upon calcium binding [5]. In addition to the EF-hand domains, these proteins also have a hydrophobic glycine/proline-rich domain, important for their translocation to the membrane. To date five members of this... 

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