The legumin precursor from white lupin seed

Identity of the subunits, assembly and proteolysis

Authors

  • Marcello DURANTI,

    Corresponding author
    1. Department of Agrifood Molecular Sciences, University of Milan, and Interuniversity Center for Studies on Informational Macromolecules (CISMI), Milan, Italy
      Correspondence to M. Duranti, Dipartimento di Scienze Molecolari Agroalimentari (DISMA), Via Celoria 2, I-20133 Milano, Italy
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  • Nicoletta GUERRIERI,

    1. Department of Agrifood Molecular Sciences, University of Milan, and Interuniversity Center for Studies on Informational Macromolecules (CISMI), Milan, Italy
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  • Paolo CERLETTI,

    1. Department of Agrifood Molecular Sciences, University of Milan, and Interuniversity Center for Studies on Informational Macromolecules (CISMI), Milan, Italy
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  • Giuseppe VECCHIO

    1. Institute of Hormone Chemistry, National Research Council of Italy, Milan, Italy
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Correspondence to M. Duranti, Dipartimento di Scienze Molecolari Agroalimentari (DISMA), Via Celoria 2, I-20133 Milano, Italy

Abstract

The precursors of the legumin-like storage protein from developing white lupin seeds (35 days after flowering) are trimers composed of protomers of Mr, 72 000 or 67 000. Some subunits of these oligomers contain processed precursor polypeptides, namely α polypeptides of either 52 000 or 44 000 linked through disulphide bonds to a β polypeptide of 21 000, typical of the mature legumin. The prolegumin is glycosylated.

Legumin oligomers purified from the same seeds are both trimers and hexamers; some of their subunits are still made of precursor polypeptides. The hexamer contains less precursor polypeptide than the trimer. A low level or absence of precursor appears to be a condition of hexamer assembly. The heterogenous prolegumin and legumin oligomers represent intermediates in the processing of the prolegumin to mature legumin.

Hydrophobic-interaction chromatography on TSK-phenyl-5PW and titration with the hydro-phobic probe 8-anilino-1-naphthalenesulphonate indicate that the legumin is less hydrophobic than the prolegumin. This is attributed to structural rearrangements at processing of the propolypeptide, made evident by the behaviour in CD and by the second-derivative ultraviolet spectra of the two proteins.

The total protein extract of developing cotyledons at 40 days after flowering contains endopeptidases, similar to those existing in the resting seeds, which cause a limited cascade degradation of the prolegumin and legumin.

Abbreviations
DAF

days after flowering

ANS

1-aniline-8-naphthalenesulphonate

HIC

hydrophobic-interaction chromatography

Ancillary