Kortt A A, Caldwell J B, Lilley G G, Higgins T J
Commonwealth Scientific and Industrial Research Organisation, Division of Biomolecular Engineering, Parkville Laboratory, Victoria, Australia.
Eur J Biochem. 1991 Jan 30;195(2):329-34. doi: 10.1111/j.1432-1033.1991.tb15710.x.
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.
已确定来自向日葵（Helianthus annuus L.）的一种富含甲硫氨酸的2S种子蛋白的氨基酸序列以及编码整个初级翻译产物的cDNA克隆的序列。成熟蛋白由一条103个氨基酸的单多肽链组成（分子量12133道尔顿），其中含有16个甲硫氨酸残基和8个半胱氨酸残基。cDNA序列表明该蛋白作为一个141个残基的前体合成，具有一个典型的25个残基的疏水信号序列，随后是一个13个残基的疏水前序列，推测该前序列在翻译后切割时被去除。成熟蛋白的序列与从cDNA推导的序列相同，在C末端没有加工的证据。将向日葵富含甲硫氨酸的蛋白序列与来自双子叶植物和单子叶植物的其他种子2S蛋白的序列进行比较，发现序列相似性有限但明显；特别是半胱氨酸残基的排列是保守的。向日葵蛋白与富含甲硫氨酸的巴西坚果2S蛋白有34%的同源性，这两种蛋白前体的前原区显示出约50%的同源性。这种相似性表明，这些富含甲硫氨酸的2S蛋白已作为仅含2 - 3%甲硫氨酸的2S蛋白超家族的一个亚类分化出来。虽然来自其他双子叶植物的相关2S蛋白被加工成一个小亚基和一个大亚基，但向日葵蛋白不以这种方式切割。
