Amino‐Acid Sequence of Feather Keratin from Fowl

Abstract

The amino acid sequence of a single polypeptide chain, B-4, from fowl feather barbs has been determined. The B-4 chain was found to consist of 96 amino acid residues and to have a molecular weight of 10206 in the S-carboxymethylated form. The N terminus of this protein was an N-acetylserine residue. The B-4 protein contained seven S-carboxymethylcysteine residues, six of which are located in the N-terminal region (residues 1 -26), and other one in C terminus. The central region of the peptide chain was rich in hydrophobic residues. There were homologous amino acids at 66 positions in the sequences of the feather keratins of fowl, emu and silver gull. The variation (substitution, deletion and insertion) in sequence was found to be localized in both terminal sections of the polypeptide chain.The B-4 protein structure was predicted to contain fi-sheet (about 30 %), turn and random-coil-like structure, and no a-helix. P-Sheet structure is mostly located in the central region (residues 22-70). On the other hand, both terminal regions are almost devoid of secondary structure.Feather proteins are solubilized in the presence of denaturant by cleavage of disulfide cross-linkages of cystine residues with oxidant or reductant [l -31. Although soluble feather keratins from various birds have been reported to be relatively homogeneous with respect to molecular weight (about 10000) [4,S], they are at the same time heterogeneous by electrophoresis and chromatography and contain slightly different components [6,7]. It was found that an extract of emu feather gave the simplest electrophoretic pattern and that from silver gull was the next simplest. Thus single polypeptide chains were isolated from feather of these two avian species [8]. The present authors have reported on isolation and characteristics of soluble proteins from fowl feather barbs and calamus [9-111. From these studies it has been found that the components of each feather keratin are almost identical in amino acid composition except for cystine and/or amide content. O'Donnell [12] and O'Donnell and Inglis [13] determined amino acid sequences of the proteins from emu and silver gull feather calami, respectively. It was found that a central section, about 60-residues long, of the polypeptide chain contained predominantly hydrophobic residues and was free of S-carboxymethylcysteine, while both terminal sections were rich in S-carboxymethylcysteine. Fraser et al. estimated from infrared spectra data that about 30 % of the polypeptide chain in seagull feather rachis had an antiparallel pleated sheet conformation [14].The ultimate purposes of the present study were to elucidate (a) the whole structure of feather keratin and (b) the relation between the feather keratin sequence and the evolutionary developments in Aves. In this paper, the amino acid sequence of the main component of fowl feather barbs is reported. The sequence is compared with those of emu and silver gull feather calami.Abbreviations. Dansyl, 1-dimethylaminonaphthalene-5-sulphonyl; HPLC, high-performan...

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