Coiled coils three-stranded

In these p-helix structures the polypeptide chain is coiled into a wide helix, formed by p strands separated by loop regions. In the simplest form, the two-sheet p helix, each turn of the helix comprises two p strands and two loop regions (Figure 5.28). This structural unit is repeated three times in extracellular bacterial proteinases to form a right-handed coiled structure which comprises two adjacent three-stranded parallel p sheets with a hydrophobic core in between. 

The first structures of this kind were reported in 1993 pectate lyase G from Erwinia chrysanthemi (Yoder et al, 1993) and alkaline protease from Pseudomonas aeruginosa (Baumann et al, 1993). Based on consideration of these crystal structures, the term parallel //-helix was introduced for a fold containing three //-strands per coil, and parallel //-roll for a fold with two //-strands per coil (Baumann etal, 1993 Yoder andjurnak, 1995 Yoder et al., 1993). The epithet parallel was intended to emphasize the distinction between these folds and the previously observed helical structure of the antibiotic gramicidin which contains both l- and D-amino acids and... 

Model peptides that can adopt the (3-sheet conformation have until recently been confined to ones that form intermolecular (3-sheets, t96,104,105 Peptides that can form intramolecular (3-sheets have been avidly sought because the coil-(3 transition1 06 in such peptides would provide thermodynamic data on the effects of sequence and individual residues on (3-sheet stability like those obtainable from model a-helical peptides. Two types of models have been developed 107 (3-hairpins, i.e. two-stranded (3-sheets, and three-stranded (3-sheets. 

Helix bundles. A third peptide chain can be added to a coiled coil to form a triple-stranded bundle.180-183 An example is the glycoprotein laminin found in basement membranes. It consists of three peptide chains which, for -600 residues at their C-terminal ends, form a three-stranded coil with heptad repeats.182184 Numerous proteins are folded into four helical segments that associate as four-helix bundles (Fig. 2-22).185-188 These include electron carriers, hormones, and structural proteins. The four-helix bundle not only is a simple packing arrangement, but also allows interactions between the + and - ends of the macro-dipoles of the helices. 

Figure 25-17 Representation of the quaternary structure of a-keratin showing (a) three a-helical polypeptide strands coiled into a rope and (b) eleven units of the three-stranded rope arranged to form one microfibril...

Coiled coils can be two-stranded, three-stranded, or four-stranded. This important structural motif has been reviewed before. 11-17 ... 

Wolf, E., Kim, P. S., and Berger, B. (1997). MultiCoil A program for predicting two-and three-stranded coiled coils. Protein Science 6, 1179-1189. 

Schneider, J. P., Lombardi, A., and DeGrado, W. F. (1998). Analysis and design of three-stranded coiled coils and three- helix bundles. Fold. Des. 3, R29-R40. 

Both the coiled coil domain and the TRAF-G domain mediate TRAF domain trimerization. The three-stranded parallel coiled coil structure is stabilized by hydrophobic residues at positions A and D of the... 

Fig. 9. Structures of soluble fragments of retrovirus TM proteins. Murine leukemia virus (MLV Fass et al, 1996) and filovirus (Weissenhom et al, 1998 Malashkevich et at, 1999) TM subunits are represented on the left by the HTLV TM structure (Kobe et at, 1999), with which they share remarkable similarity. Human and simian lentivirus TM subunits (Weissenhom etat, 1997 Chan etat, 1997 Caffrey etat, 1998) are represented by the structure of SIV TM on the right. Both structures are hairpins containing central three-stranded coiled coils surrounded by buttressing regions that pack into the grooves on the outsides of the coiled coils. The amino acid side chains in the conserved cysteine-rich motif of HTLV TM are shown as space-filling atoms and labeled according to their positions in the motif.

Lee K-H, Cabello C, Henuningsen L, Marsh ENG, Pecoraro VL. Using nonnatural amino acids to control metal-coordination number in three-stranded coiled coils. Angew. Chem. Int. Ed. 2006 45 2864-2868. 

The formation of three-stranded, helical (synthetic) proteins has been shown to be influenced by metal-ion binding to ligands that form part of the component peptide strands. In one study of this type, a 15-residue amphiphilic peptide containing a 2,2 -bipyridine derivative situated at the N-terminus was demonstrated to self-assemble spontaneously in the presence of selected transition metal ions to form a 45-residue metalloprotein with a triple-helical, coiled-coil structure. 

Crick (1952) pointed out that this difficulty could be overcome by supposing that the a-helices in a-keratin were distorted in a helical manner to form coiled coils as illustrated in Fig. 14. This distortion, which was claimed to require only about 0.1 kcal per residue, enabled the side chains to pack more neatly. In subsequent papers Crick obtained an expression for the Fourier transform of a coiled coil (Crick, 1953a) and was able to show that this type of distortion could account in a general way for some previously unexplained features of the X-ray pattern of a-keratin (Crick, 1953b) including the simultaneous appearance of 1.5 and 5.15 A meridional reflections. Detailed descriptions of two-strand and three-strand ropes of these coiled coils were given in which the pitch of the major helix was 186 A, and it was suggested that the three-strand model was appropriate... 

Fic. 14. (a) Distribution of residues in the three-strand coiled-coil rope. For clarity only one coiled coil is shown, (b) Distribution of residues in an undistorted a-helix. 

In an attempt to reconcile the microfibrillar structure and the X-ray diffraction pattern with the coiled-coil hypothesis Swanbeck (1961) proposed a model in which a central three-strand coiled coil was surrounded further by four concentric layers of a-helices, the tilt increasing progressively up to a value of 50° in the outer layer of nineteen chains. In a later more detailed description (Swanbeck, 1963) it was proposed that the three inner layers consisted of a-helices of pitch 5.25, 5.65, and 6.40 A, that the fourth layer consisted of 3.0w helices (Donohue, 1953) and the outer layer was a 3-structure. 

FIGURE 10-6 Schematic views of compound helices and their packing. Left, a coiled coil, se n-strand cable and three-strand rope right, packing diagram for coils and caWcs in a-keratin. [From Corey and Pauling, Proc, International Wool Textile Res, Conf, Australia 1955, Vol. B, 249-66.]... 

Wolf E, Kim PS, Berger B. MultiCoil a program for predicting two- and three-stranded coiled coils. Prot Sci 1997 6 1179-1189. 

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