EF motif

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...

OFF) motif, and the edge-to-face (EF) motif. In the OFF geometry, the molecules are exactly or closely parallel but are offset so that the oppositely charged regions of the molecules are closest. In the EF motif (sometimes vertex-to-face, sometimes called T-shaped) the relatively positive hydrogenic rim is directed toward the central negative n-electron density. 

Fig. I The offset-face-to-face (OFF) and edge-to-face (EF) motifs for benzene. (View this art in color at www.dekker.com.)...

In Fig. 2. it is noticeable that there is variation in the angle between arene planes in the EF motifs. This is characteristic of aromatic-aromatic intermolecular motifs there is little variation in energy vrith angle, and the concept of a continuous range of stability between the parallel OFF motif and the angled EF motif is valid. Aromatic-aromatic intermolecular potentials are soft. 

In this section, some of the diversity and scope of aromatic—aromatic interactions is illustrated. For example, the curved surfaces of Cgo and other fullerenes are known to engage in parallel and obliqne interactions with other arenes, mimicking the OFF and EF motifs. ... 

Metallocene molecules, such as the prototype ferrocene 5. pack in crystals mainly with EF motifs, similar to the crystal packing of benzene. 

The examples so far involve independent aromatic moieties, freely able to arrange into OFF and EF motifs. There are also chemical systems in which the aromatic component is a substituent or is part of a more elaborate molecule. In these the mutually dependent configurations and conformations of the aromatic groups influence the intermolecular interactions they can form. A considerable number of classes of compounds allow synergy of individual aromatic-aromatic interactions, and the generation of concerted sets of OFF or EF motifs. These are termed embraces, because they are multi-armed, mutual, concerted, and attractive. Some of the principal types of embrace are outlined here for representative molecules. 

The fourfold analog of the sixfold embrace just described is shown in Fig. 13 four phenyl rings are engaged in a conceited cycle of four EF motifs. This occurs mainly with Ph4E systems, for which the relationship between the two molecules involved is simple translation, and infinite chains with a repeat of just one molecule occur in crystals. 

This involves two aryl groups on each molecule, and usually it is centrosyminetric. As shown in Fig. 14a,b, there is an OFF motif between two groups, each of which is also donor in an EF motif. The (OFF)(EF)2 embrace is also named the parallel fourfold phenyl(aryl) einbrace, to differentiate it from the orthogonal fourfold phenyl embrace. (EF)4. " As the size of a heteroaromatic ligand increases, as in eilatin. the OFF motif in the embrace becomes dominant (Fig. 14c), and the association of the complexes [Ru(phen)2(eilatin)] in acetonitrile is measurable. 

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. 

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

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... 

Figure 11.9 (Left) The EF hand helix-loop-helix motif (centre) rat testes calmodulin. The globular domains each have two Ca2+-binding sites, indicated by white spheres, connected by a seven-turn a-helix (right) two views of the (Ca2+)4 fruit fly calmodulin in complex with its 26-residue target peptide from rabbit skeletal muscle myosin light chain kinase, ((left, centre) From Voet and Voet, 2004. Reproduced with permission from John Wiley Sons., Inc. and (right) Carafoli, 2002. Copyright (2002) National Academy of Sciences, USA.)...

Most of the EF-hand motifs have one water (—X). On the other hand, in Rhizopus chinensis aspartic proteinase (Suguna et al., 1987) there is one main-chain carbonyl oxygen bound to calcium and six water molecules to complete the pentagonal bipyramidal coordination. Calcium coordination has been measured in several viruses, such as Southern bean mosaic virus (Silva and Rossmann, 1985), satellite tobacco necrosis virus (Jones and Liljas, 1984), and tomato bushy stunt virus IV (Olson et al., 1983). 

Helix-loop-helix (HLH) or EF-hand" motif in -binding sites. The Ca " ligands are part of a 12-residue loop flanked by orthogonal a helices. 

The amino-terminal domain is on the left the carboxyl-terminal domain on the right, (b) Calmodulin associated with a helical domain (red) of one of the many enzymes it regulates, calmodulin-dependent protein kinase II (PDB ID 1CDL). Notice that the long central a helix visible in (a) has bent back on itself in binding to the helical substrate domain. The central helix is clearly more flexible in solution than in the crystal, (c) Each of the four Ca2+-binding sites occurs in a helix-loop-helix motif called the EF hand, also found in many other Ca2+-binding proteins. 

E (entgegen) configuration 43 E3 binding protein 796 Eadie-Hofctee plot 460 E-cadhedrin 574 Echinodermata 25 Ectoderm 23 Ectoenzymes 409 Ectopic proteins 573 Edelman, Gerald M. 84 Edman degradation 118 EDTA. See Ethylenediaminetetraacetic acid Effector(s) of allosteric enzymes 473-475 EF-hand motif 313, 317 EGF (epithelial growth factor), definition of 577... 

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