Structure characterization of polypeptides of viscous glycoprotein from yam (Dioscorea opposita Thunb.) mucilage
2001
Tsukui, M. (Kanto Gakuin Women's Junior Coll., Yokohama (Japan)) | Sato, H. | Nagashima, T. | Watanabe, T. | Takano, K. | Kozima, T.T.
In this study, partial structure of polypeptide chains of glycoprotein responsible for viscosity from three kinds of yams (Tsukuneimo, Ichoimo and Nagaimo) was characterized. The N-terminal amino acid sequences of 32- and 28-kDa glycoproteins obtained from SDS-PAGE in the absence of 2-mercaptoethanol (2-ME) were determined as V-E-D-E-F-S-Y-I-E-G-N-P-N-G-P-E-N-W-G-N. The N-terminal amino acid sequences of 56-kDa glycoproteins from Tsukuneimo and Ichoimo were identical, D-G-D-F-S-Y-I-E-G-S-P-N-G-P-E-N-W-G-N-L, whereas the N-terminal sequence (D-E-D-D-F-S-Y-I-E-G-S-P-N-G-P-E-N-W-G-N) for that from Nagaimo was different from it. On the database search via World Wide Web network, a consensus sequence, obtained from these sequences, was similar with that of dioscorin, one of the storage proteins of yam. On the SDS-PAGE in the presence of 2-ME, the glycoproteins demonstrated one peptide band with molecular mass of 32kDa. Based on N-terminal amino acid sequence analysis, the 32-kDa peptide was identified as mixture of two kinds of polypeptides, designated as 32-kDa (A) for the dominant peptide and 32-kDa (B) for the minor peptide. Consequently three proteins obtained by non-reduced SDS-PAGE were concluded as follows ; the 56-kDa glycoprotein consisted of two 32kDa (B) joined by disulfide bond, the 32-kDa glycoprotein was monomer of 32kDa (A) without any disulfide bonds, and the 28-kDa glycoprotein was monomer of 32-kDa (A) whose apparent molecular mass was decreased due to internal disulfide bond. The peptide mapping analysis using limited proteolysis and amino acid composition analysis for 32-kDa (A) peptide suggested that the glycoproteins of three yams had slightly different primary structure.
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