Alteration of the structural properties of starch components by the lack of an isoform of starch branching enzyme in rice seeds.
Alteration of the structural properties of starch components by the lack of an isoform of starch branching enzyme in rice seeds.
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DOI：
10.1016/s0021-9258(17)46738-x
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发表时间：
1993-09
期刊：
影响因子：
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通讯作者：
K. Mizuno;T. Kawasaki;H. Shimada;Hiroaki Satoh;Eiki Kobayashi;S. Okumura;Y. Arai;T. Baba
中科院分区：
文献类型：
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作者：
K. Mizuno;T. Kawasaki;H. Shimada;Hiroaki Satoh;Eiki Kobayashi;S. Okumura;Y. Arai;T. Baba
本研究描述了淀粉合成酶对水稻直链淀粉延伸突变体（含有结构异常的支链D-葡聚糖）中贮藏淀粉生物合成的影响。蛋白质印迹分析表明，五个直链淀粉延伸突变株系中有两个缺乏淀粉分支酶的亚型，称为RBE 3，尽管颗粒结合淀粉合成酶和分支酶的主要形式RBE 1的水平在这两个突变体中是正常的。对应于87-kDa RBE 3分子的蛋白质存在于其他三种直链淀粉延伸剂突变体以及野生型中。然而，分支酶活性的水平显着下降，在所有的直链淀粉扩展剂突变体，这表明在这三个突变体中的87-kDa的蛋白质是无活性形式的RBE 3。因此，我们得出结论，在直链淀粉延伸剂突变体的水稻异常分支葡聚糖的形成是由于缺乏RBE 3活性。用合成的寡核苷酸作探针，从λ gt 11的正常水稻种子cDNA文库中鉴定了编码RBE 3的cDNA克隆。推导的氨基酸序列表明，该蛋白最初合成为825个氨基酸的前体，包括在NH 2末端的65个残基的转运肽。淀粉分解酶的催化区域的序列在RBE 3的序列中高度保守。因此，分支酶同种型属于淀粉分解酶家族。RBE 3还与RBE 1具有明显程度的序列同一性，尤其是在蛋白质分子的中心部分。然而，与RBE 1相比，RBE 3在NH 2末端具有约70个残基的额外序列，并且缺少约50个残基的COOH末端序列。两个末端的结构差异可以解释RBE 1和RBE 3在淀粉合成中的不同作用。
This study describes the effect of starch-synthesizing enzymes on biosynthesis of storage starch in rice amylose-extender mutants, which contain branched D-glucans with abnormal structures. Western blot analysis indicated that two out of five amylose-extender mutant lines lacked an isoform of starch branching enzyme, termed RBE3, although the levels of granule-bound starch synthase and a major form of branching enzyme, RBE1, were normal in these two mutants. Proteins corresponding to the 87-kDa RBE3 molecule were present in the three other amylose-extender mutants as well as in the wild type. However, the level of branching enzyme activity significantly decreased in all amylose-extender mutants, suggesting that the 87-kDa proteins in these three mutants are inactive forms of RBE3. Therefore, we conclude that formation of the abnormal branched glucans in the amylose-extender mutant of rice is due to the lack of the RBE3 activity. The cDNA clones encoding RBE3 have been identified from a normal rice seed cDNA library in lambda gt11, using a synthetic oligonucleotide as a probe. The deduced amino acid sequence of RBE3 indicates that this protein is initially synthesized as a precursor of 825 amino acids, including a 65-residue transit peptide at the NH2 terminus. The sequences of the catalytic regions in amylolytic enzymes are highly conserved in the sequence of RBE3. Thus, the branching enzyme isoform belongs to a family of the amylolytic enzymes. RBE3 also shares a noticeable degree of sequence identity with RBE1, especially at the central portion of the protein molecule. However, RBE3 possesses an approximately 70-residue extra sequence at the NH2 terminus and lacks a COOH-terminal sequence of almost 50 residues as compared with RBE1. The structural differences at both termini may explain the distinct role in starch synthesis for RBE1 and RBE3.