Structural studies on the microfibrillar proteins of wool. Interaction between alpha-helical segments and reassembly of a four-chain structure.
The alpha-helix-rich particle of Mr 50 200, derived by limited alpha-chymotryptic digestion of the solubilized microfibrillar proteins from wool alpha-keratin, consists mainly of polypeptide-chain segments of Mr 12 500 (fraction ChC) and 25 000 (fraction ChB). The 12 500-Mr segments are of two types (I and II), which are derived from different polypeptide chains of the microfibrillar complex. Each of these type-I and type-II segments partially self-associates in benign solvents to form either dimers or tetramers. When mixed, the two segments show changes in physical properties (alpha-helix content, difference spectra and molecular weight) indicative of complex-formation. The maximum changes occur when the two segments are mixed in an equimolar ratio. Complexes isolated after rapid dialysis of mixtures from 8 M-urea solution were examined by various methods. A tetrameric structure is the main product formed in all cases, and the maximum amount of tetramer is obtained from equimolar mixtures of the type-I and type-II polypeptides. When urea is removed by dialysis from the unfractionated 12 500-Mr segments (fraction ChC) or from the alpha-helix-rich particle itself, a similar complex of Mr 50 000 is formed. The physical properties of these reconstituted entities (alpha-helix content, molecular weight, thermal stability and exposure of tyrosine residues) are similar to those of the original alpha-helix-rich particle. Cross-linking experiments with dimethyl suberimidate are in agreement with a four-chain complex for the reassembled structures. A pair of double-stranded alpha-helices is proposed for the particle, and is considered to be an integral part of the microfibrillar complex in wool alpha-keratin.
D000818:Animals; D002850:Chromatography, Gel; D003285:Contractile Proteins; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004120:Dimethyl Suberimidate / Q000494:pharmacology; D004547:Elastic Tissue / Q000032:analysis*; D004591:Electrophoresis, Polyacrylamide Gel; D016326:Extracellular Matrix Proteins; D046911:Macromolecular Substances; D008970:Molecular Weight; D010455:Peptides / Q000032:analysis; D011489:Protein Denaturation; D000072260:RNA Splicing Factors; D013053:Spectrophotometry; D014935:Wool / Q000032:analysis*
D003285:Contractile Proteins; D003432:Cross-Linking Reagents; D016326:Extracellular Matrix Proteins; D046911:Macromolecular Substances; D010455:Peptides; D000072260:RNA Splicing Factors; C016598:microfibrillar protein; D004120:Dimethyl Suberimidate