title: Amino acid and cDNA sequences of a methionine-rich 2S protein from sunflower seed (Helianthus annuus L.).
abstract: The amino acid sequence of a methionine-rich 2S seed protein from sunflower (Helianthus annuus L.) and the sequence of a cDNA clone which codes for the entire primary translation product have been determined. The mature protein consists of a single polypeptide chain of 103 amino acids (molecular mass 12133 Da) which contains 16 residues of methionine and 8 residues of cysteine. The cDNA sequence established that the protein is synthesized as a precursor of 141 residues with a typical hydrophobic signal sequence of 25 residues followed by a further 13-residue hydrophobic pro-sequence which is presumably removed by post-translational cleavage. The sequence of the mature protein and that deduced from the cDNA were identical with no evidence of processing at the C-terminus. Comparison of the sunflower methionine-rich protein sequence with sequences of other seed 2S proteins from dicotyledons and monocotyledons showed limited but distinct sequence similarities; in particular the arrangement of the cysteine residues was conserved. The sunflower protein shows 34% identity with the methionine-rich Brazil nut 2S protein and the prepro regions of the precursors of these two proteins show about 50% identity. This similarity indicates that these methionine-rich 2S proteins have diverged as a subclass of the 2S superfamily of proteins which contain only 2-3% methionine. While the related 2S proteins from other dicotyledons are processed to a small and large subunit, the sunflower protein is not cleaved in this way.
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation, Division of Biomolecular Engineering, Parkville Laboratory, Victoria, Australia.
authors.forename: A A
authors.initials: AA
authors.lastname: Kortt
authors.forename: J B
authors.initials: JB
authors.lastname: Caldwell
authors.forename: G G
authors.initials: GG
authors.lastname: Lilley
authors.forename: T J
authors.initials: TJ
authors.lastname: Higgins
mesh_terms: D055516:2S Albumins, Plant; D000595:Amino Acid Sequence; D052179:Antigens, Plant; D001483:Base Sequence; D003001:Cloning, Molecular; D004247:DNA / Q000737:chemistry*; D006368:Helianthus / Q000235:genetics*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010940:Plant Proteins / Q000235:genetics*; D011487:Protein Conformation; D021382:Protein Sorting Signals / Q000235:genetics; D012333:RNA, Messenger / Q000737:chemistry; D012639:Seeds / Q000235:genetics*; D012995:Solubility
chemical_list: D055516:2S Albumins, Plant; D052179:Antigens, Plant; D010940:Plant Proteins; D021382:Protein Sorting Signals; D012333:RNA, Messenger; C067568:methionine-rich 2S protein, Helianthus; D004247:DNA