Hydrogen-Bonded Helices

Fig. 22. The Fox and Richards model of the alamethicin transmembrane channel shown diagrammatically. Interruption of the oc-helical hydrogen bonding by the Pro-14 residue is signified by representation of each monomer as two cylindrical sections. The stippled spheres at the mouth of the channel represent the Glu-18, the spheres at the centre the Gln-7, and the spheres at the top the Gln-19 residues. Fox, R. O., Richards, F. M. Reprinted by permission from Nature 300, 325 (1982). Copyright Macmillan Journals Limited...

Fig. 3 Helical hydrogen bonded chain structure formed between [15]crown-5 and [La(N03)3 (H2O)2(l,10-phenanthroline)].[24]... 

A ferris wheel assembly involving a 1 1 complex of 19 and metallated [18]crown-6 is found in the cationic supermolecule [La(H20)3([ 18]crown-6)] (19+2H) + [48]. The lanthanum ion is coordinated by one calixarene sulfonate group, the [18] crown-6 and three aquo ligands, and the metallated crown sits inside the calixarene cavity. A helical hydrogen bonded chain structure is formed between the cationic assembly, water and chloride ions. The ferris wheel structural motif is also found in Ce3+ complex which simultaneously contains a Russian Doll assembly [44]. 

Fig. 11. Drawing of a typical a-helix, residues 40-51 of the carp muscle calciumbinding protein. The helical hydrogen bonds are shown as dotted lines and the main chain bonds are solid. The arrow represents the right-handed helical path of the backbone. The direction of view is from the solvent, so that the side groups on the front side of the helix are predominantly hydrophilic and those in the back are predominantly hydrophobic.

Fig. 16. An unusual interrupted helix from subtilisin (residues 62-86), in which the helical hydrogen bonds continue to a final tum that is formed by a separate piece of main chain. Such interrupted helices (broken on one side of the double helix) are apparently a fundamental feature of nucleic acid structure as illustrated by tRNA, but are exceedingly rare in protein structure.

Fig. 18. An example of the an conformation at the end of the A helix in myoglobin (residues 8-17). The normal a-helical hydrogen bonds are shown dotted, while the tighter a, bond is shown by crosses.

Fig. 55. Two very similar 5-residue turns with a single a-helical hydrogen bond (a) pancreatic trypsin inhibitor residues 24-28, stabilized by the side chain of Asn-24 (b) prealbumin residues 18-22, stabilized by Asp-18.

In the crystal structures, neighboring doublehelices have the same rotational orientation and the same translation of half a fiber repeat as in the PARA 1 model. Only the Ax vector is slightly larger in the calculated interaction (1.077 nm) than in the observed ones 1.062 nm and 1.068 nm in the A type and B type, respectively. This may be due to the fact that in the crystal structures the helices depart slightly from perfect 6-fold symmetry. Also, no interpenetation of the van der Waals surfaces is allowed in the calculations, whereas some of them may occur in the cristallographic structure. It is quite interesting to note that the network of inter double-helices hydrogen bonds found in the calculated PARA 1 model reproduces those found in the crystalline structures. 

Much of their backbone chain is Involved in helical hydrogen-bonded associations. Folding is maintained by both internal hydrogen and hydrophobic bonds as well as by disulfide bonds. 

Figure 16. Cross section of an associated curdlan micelle showing the triple helices hydrogen bonded to the inaccessible water of crystallization...

Fig. 5 (a) Side view of the helical hydrogen bonded structure of 4 in the solid state. Top views of the crystal packing of 4 capped sticks (b) and space filling representation (c)... 

When the racemic heterohelicenediol (PAf)-S4 forms an inclusion complex with EtOH through helical hydrogen bonding, the interplanar angle decreases to 37.96° <1995CC1873>. 

Figure 23. (a) 1,3,5-Benzene trisamides that form columns in apolar solvents via 3-fold intermolecular hydrogen bonding (b) solid state arrangement of the helical columns (c) graphical representation of the helical hydrogen-bonded columns. (Reprinted with permission from ref 202. Copyright 1999 Royal Society of Chemistry.)... 

Some phenols [128-130] crystallize with a hydrogen-bond helix 23 a, in which the molecules are interlinked about a 3,-axis of length 4.6 A. Phenol itself [131], o-cresol [132] and m-cresol [133] form helical hydrogen-bond arrays along a (pseudo) threefold axis of length 6 A, as shown in 23b. 

Solvated helical peptide folding charge-charge separation, 304 concrete folding mechanism, 307 equilibrium constant, 305 free energy, 306 a-helical hydrogen bonds, 307 Lennard Jones interactions, 308 radius of gyration, 306 relaxation time, 305... 

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