EF-hand

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 6.21 Schematic diagram of the conformational changes of calmodulin upon peptide binding, (a) In the free form the calmodulin molecule is dumhhell-shaped comprising two domains (red and green), each having two EF hands with bound calcium (yellow), (b) In the form with bound peptides (blue) the a helix linker has been broken, the two ends of the molecule are close together and they form a compact globular complex. The internal structure of each domain is essentially unchanged. The hound peptide binds as an a helix.

Figure 6.21a) comprising two domains separated by a long straight a helix, similar in shape to troponin-C described in Chapter 2 (see Figure 2.13c). Each domain comprises two EF hands (see Figure 2.13a), each of which binds a calcium atom. The two domains are clearly separated in space at the two ends of the a helix linker. 

FIGURE 17.19 ff-Acdnin exists as a homodimer of andparallel snbnnits, illnstrated here in terms of their primary strnctnre. The N-ter-miiral, actin-binding domain and the C-termi-nal, EF-hand domains are separated by a central domain consisting of four repeats of a 122-residne sequence. 

Why does EDTA cause only 90% inhibition, leaving 10% of the activity intact Buffer solutions usually contain 0.1 1 pM of contaminating Ca2+ when special precaution is not taken, and this concentration is much greater than the molar concentration of luciferase used in the experiments. Thus, one of the possibilities would be that Ca2+ interacts with the molecule of luciferase and can increase the activity of luciferase about 10 times, in spite of the fact that the molecule of luciferase lacks the Ca2+ binding site of EF-hand type (Thompson et al., 1989). Another possibility would be that EDTA interacts directly with the molecules of luciferase, to cause the inhibition. The question remains unresolved. 

According to Charbonneau et al. (1985), aequorin is a single chain peptide consisting of 189 amino acid residues, with an unblocked amino terminal. The molecule contains three cysteine residues and three EF-hand Ca2+-binding domains. The absorption spectra of aequorin and BFP are shown in Fig. 4.1.3, together with the luminescence spectrum of aequorin and the fluorescence spectrum of BFP. 

Non-EF-hand Ca2+-binding proteins including the annexins, C2-domain proteins, and gelsolin, and the EF-hand Ca2+-binding proteins. 

This review will focus on the large family of EF-hand proteins characterized by a common structural motif, the EF-hand (Fig 1). 

Calretinin is homologous to calbindin D28k- It is abundantly expressed in the central and peripheral nervous system and other organs. The protein contains four EF-hand domains homologous to the first four of calbindin D28k-... 

The Ca2+-binding subunit TN-C is homologous to calmodulin with four EF-hands. In contrast to calmodulin, which is ubiquitously expressed in multicellular eukaryotic organisms and interacts with many targets, troponin specifically regulates muscle contraction. There are some structural differences between Troponin C in skeletal and cardiac muscles reflecting their physiological differences. 

This family contains more than 40 members subdivided into five subfamilies [4]. The NCS have been involved in phototransduction and regulation of neurotransmitter release. The NCS have two pairs of EF-hands and, unlike CaM and SI00 proteins, possess a consensus myristoylation sequence at the N-terminal responsible for the targeting of the NCS to the membrane. 

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... 

ALG-2 is the fust calcium-binding protein of the EF-hand family found to be directly involved in apoptosis. ALG-2 is a 22 kDa protein and like the other members of the penta EF-hand family, contains five EF-hands, with only two of them functional. ALG-2 protein is expressed in the brain and eye and was found to be upregulated in various cancer tissues. Several targets have been found, such as proteins AEP, Alix, preflin, and annexins, suggesting a putative role of ALG-2 in apoptosis. 

Calcineurin homologous protein (CHP) is ubiquitously expressed and has four EF-hand domains and one putative site of myristoylation. 

Kawasaki H, Nakayama S, Kretsinger RH (1998) Classification and evolution of EF-hand proteins. Biometals 11 277-295... 

Krebs J, Heizmann CW (2007) Calcium-binding proteins and the EF-hand principle. In Krebs J, Michalak M (eds) Calcium a matter of life and death, New Comprehensive Biochemistry, vol 41 (Series Bernardi G). Elsevier, pp 51-93... 

Maki M, Kitaura Y, Satoh H et al (2002) Structures, functions and molecular evolution of the penta-EF-hand Ca2+-binding proteins. Biochim Biophys Acta 1600 51-60... 

All PLC isozymes have conserved catalytic domains designated X and Y, and a C2 domain similar to that in cPLA2 (Fig. 2). In addition, the (3, y and 8 isozymes have pleckstrin homology (PH) domains and EF-hand domains located in theN-teiminal region. The y isozymes differ in that they have Src homology domains (SH2 and SH3) and an additional PH domain split by the SH domains. The (3 and y isozymes are of140-155 kDa mass, whereas the 8 isozymes are smaller (85 kDa) and the o isozyme is larger (240 kDa). 

TPR) domains. PP2B (calcineurin) is a heterodimer of a catalytic A-subunit together with a regulatory, Ca2+-binding B-subunit. The A-subunit additionally carries a calmodulin binding site and an autoinhibitory domain. PP7 also contains EF-hand motifs. Both, PP2B and PP7 are stimulated by Ca2+-ions. 

S100 proteins (named because of their solubility in a 100% ammonium sulfate solution) constitute the largest family within the EF-hand Ca2+-binding proteins superfamily [1]. SI00 proteins are small, acidic proteins containing two distinct Ca2+-binding EF-hand structural motifs [2]. The C-terminal EF-hand contains the... 

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