Molecules of intermediate filament (IF) proteins contain a central rod domain in which the two constituent chains have a predominantly α-helical conformation and are coiled around one another to form segments of two-strand rope. Possible interactions between the two long segments, termed 1B and 2 were investigated by a technique successfully employed in studies of the modes of association of collagen molecules by Miller and coworkers. Prominent maxima were found in all of the six possible modes of association between the rod domain segments in individual IF proteins and certain maxima were found to be common to all IF. The surface lattice of the IF from α-keratin has been determined and possible bonding arrangements between the rod-domain segments are catalogued. A systematic search was carried out for combinations of interaction maxima which were consistent with the dimensions of the surface lattice. By the further application of stereochemical constraints, models for the topological arrangement of the rod-domain segments on the surface lattice were derived and these are illustrated and discussed.

Fragments of α-keratin were obtained by partial proteolysis of the low-sulphur protein fraction, S-carboxymethylkerateine-A, from wool. X-ray diffraction and infrared absorption studies were made on oriented films formed from these fragments. The results indicate that the fragments have a coiled-coil α-helical conformation similar to that in α-keratins, and that the films consist of particles approximately 160 Å in length arranged end-to-end.

The complete amino acid sequence of one of the two major components comprising the rachis and calamus of emu (D. novae-hollandiae) feather keratin has been determined.

Isotope editing of amide infrared bands not only localises secondary structural elements within the protein but also yields conformational information that is not available from the linear dichroism of aligned samples without isotope editing. The additional information that can be derived on the orientational distribution of α-helices in membranes by the combined use of different amide bands and several positions of labelling is presented here. Also, the relationship between the azimuthal orientation of the transition moment and the protein structure is treated explicitly. A comprehensive analysis of the infrared dichroism for β-sheets and β-barrels is given here, for the first time. The orientation of the individual transition moments in a β-sheet that is essential for this analysis is derived for the different amide bands.

AbstractA comparison has been made of the intrachain potential energy of an infinite straight α‐helix of poly‐L‐alanine with that of the distorted form adopted in a coiled coil conformation. The energy terms included were the van der Waal's, electrostatic, hydrogen‐bond, and the rotational potential terms. The results indicate that the potential energies of the structures investigated are almost the same, and so a transformation from one state to another may occur without significant changes in potential energy. Particular care has been taken to ensure that the electrostatic and van der Waal's interaction terms are fully convergent. The values obtained for the α‐helix were compared with those already published, and some significant differences were found.

The interchain packing energy of two-, three-, and four-stranded α-helical ropes has been investigated. Poly- L -alanine was chosen as a model, and the interchain energies were calculated for various combinations of chain sense as a function of interchain distance, axial orientation and displacement. For comparison, the packing energies of the analogous assemblies of straight α-helices were also computed. Only those systems in which the chains were equivalent, i.e., related by line symmetry, were considered. The results indicate that for structures in which all the chains are equivalent the interchain packing energy favors the coiled coil arrangements.

A series of poly( L ‐glutamic acid) esters have been synthesized and studied by optical rotatory dispersion, x‐ray diffraction, and infrared spectrometry. The results obtained emphasize the importance of the outer portions of the side chains in determining both the stability and precise conformation of the α‐helix.

A series of poly( L -glutamic acid) esters have been synthesized and studied by optical rotatory dispersion, x-ray diffraction, and infrared spectrometry. The results obtained emphasize the importance of the outer portions of the side chains in determining both the stability and precise conformation of the α-helix.

A series of polypeptides containing ordered sequences of glyeyl and γ‐ethyl L ‐glutamyl residues has been synthesized. The properties of the polymers were investigated by x‐ray diffraction, infrared spectrophotometry, and optical rotator dispersion, and the results indicate that glycine appreciably reduces the stability of the γ‐ethyl L ‐glutamate helix.

A detailed analysis of the infra-red spectrum of silk fibroin has been made using polarized radiation. The various components of the Amide I and Amide A bands were separated using an iterative least squares procedure and integrated intensities and transition moment directions were determined. The half band widths of the Amide I components were found to depend on the orientation of the transition moments with respect to the silk crystallites and could be correlated with the crystallite dimension determined from the breadths of the equatorial X-ray reflections. The transition moment of the Amide I band was found to be inclined at an angle of 19° to the direction of the CO bond, in agreement with values predicted from studies of model compounds.

The β-keratin chain with four 34-residue repeats that is conserved across the lepidosaurs (lizards, snakes and tuatara) contains three linker regions as well as a short, conserved N-terminal domain and a longer, more variable C-terminal domain. Earlier modelling had shown that only six classes of structure involving the four 34-residue repeats were possible. In three of these the 34-residue repeats were confined to a single filament (Classes 1, 2 and 3) whereas in the remaining three classes the repeats lay in two, three or four filaments, with some of the linkers forming interfilament connections (Classes 4, 5 and 6). In this work the members of each class of structure (a total of 20 arrangements) have been described and a comparison has been made of the topologies of each of the linker regions. This provides new constraints on the structure of the chain as a whole. Also, analysis of the sequences of the three linker regions has revealed that the central linker (and only the central linker) contains four short regions displaying a distinctive dipeptide repeat of the form (S-X)2,3 separated by short regions containing proline and cysteine residues. By analogy with silk fibroin proteins this has the capability of forming a β-sheet-like conformation. Using the topology and sequence data the evidence suggests that the four 34-residue repeat chain adopts a Class 4a structure with a β-sandwich in filament 1 connected through the central linker to a β-sandwich in filament 2.

A series of polypeptides containing ordered sequences of S-benzyl-L-cysteinyl (C) and γ-ethyl-L-glutamyl (G) residues has been synthesized. Optical rotatory dispersion measurements show that all the polymers adopt some degree of helical conformation in solution. Using polarized infra-red spectrometry α-helical material could be detected in films of all the polymers, as in solution, but always in lower amount than in the parent (G2)n homopolymer†. The polymers (G3CG)n, (GCG)n and (GCG2)n gave α-type X-ray diffraction patterns; the remainder gave β-type patterns. In general the stability of the α-helix is lowered by the introduction of C residues. It is suggested that this is due to an unfavourable side chain—main chain interaction.

The study of the effect of pH on the behaviour of proteins is still a topic of interest. We here report an unexpected increase of thermal stability of hard alpha-keratins under the influence of pH that is observed when investigating their thermal behaviour by differential scanning calorimetry (DSC). The results, particularly for oxidatively damaged keratin fibres treated with low pH solution, show a significant increase of enthalpy and a shift of the peak temperature towards higher temperature for the endothermic process assigned to the thermal denaturation. We propose a three-phase model for describing the behaviour of fibrous hard alpha-keratins, in which the interface, made of non-helical tail domains of keratin, scaffolds the intermediate filaments and plays an important role. It is strengthen by the action of strong acids and controls the thermal properties of the alpha-helix. The approach is supported by amino-acid analysis, X-ray diffraction, Raman spectroscopy and tensile strength observations.