Structural Studies on the Microfibrillar Proteins of Wool: Characterization of the a-Helix-Rich Particle Produced by Chymotryptic Digestion

Abstract

The oc-helix-rich particle produced bychymotryptic digestion of the reduced and alkylated microfibrillar proteins of wool was characterized by physicochemical methods. The preparations were homogeneous with respect to size and the particle molecular weight was found to be 50200 ± 2 000.Hydrodynamic methods indicated a length of about 20 nm for the particle. The properties of the particle, derived from two methods of isolation of the microfibrillar proteins, were identical and were also independent of the type of wool used. From a consideration of the molecular weight in denaturing solvents and from cross-linking experiments with dimethyl suberimidate a four-chain structure, consisting of a pair of double-stranded oc-helices, is proposed for the particle.

Intermediate filaments in alpha-keratins.

“…4b. This pattern exhibits the observed association between 1B segments (27) and also involves associations between pairs of antiparallel molecules that are approximately in register. This is consistent with a known form of in vitro association that leads to particles about 480 A in length (21, 22, 28).…”

“…Studies of helix-rich particles isolated from partial hydrolysates of wool IF indicate that strong association exists between the 1B segments of neighboring molecules (27), and the arguments presented in the previous section suggest that the interaction is most likely to be of the (1BU, 1BD) variety. If the pair of molecules associated by means of this interaction are symmetrically disposed about the lattice point at z = 0 (Fig.…”

“…This is consistent with a known form of in vitro association that leads to particles about 480 A in length (21, 22, 28). The mean Biochemistry: Fraser et in a natural way for the observed lB-lB interaction (27) and for two-molecule aggregates with a length around 480 A (21,22,28).…”

Epidermal α-Keratin: Structure and Chemical Composition

“…Laek of" stuttering" of hydrophobie heptads Expression of ehains in pairs Sun et al 1983 (epidermis and other epithelia) iour of the IX-helical regions of wool IX-keratin chains supported the proposed tetrameric structure (Woods and Gruen 1981;Gruen and Woods 1983) and similar cross-linking experiments gave rise to tetramers from the IX-helical regions of desmin and the epidermal IX-keratin of bovine hoof (Gruen and Woods 1983). It should be noted, however, that even the last pro tein is not strictly comparable with that upon wh ich the earlier pro tein cleavage work was performed, as bovine hoof epidermis lacks a group of high MW IX-keratin chains present in the sn out epidermis (Sect.…”

“…1 the filament could in fact have a "core" of lesser density compatible with the extensive data for a ring-co re structure and the essential difference between the two models would then be in the arrangement of subunits around the core. An advantage of the tetragonal arrangement is that, by requiring specific lateral aggregations of coiled-coils at a subtonofilament level it may more readily accommodate evidence such as that for the presence of overlapping dimers of three-stranded (Skerrow 1974;Steinert et al 1976) or two-stranded (Ahmadi and Speakman 1978;Woods and Gruen 1981;Gruen and Woods 1983) coiled-coils.…”