Occurrence of Multiple Forms for Starch Synthase II Isozyme in Developing Seeds of Kidney Bean

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Starch synthases contribute to the elongation of glucan chains during starch synthesis, and therefore their characteristics are one of the dominant factors influencing the fine structure of starch. To understand the detailed properties of starch synthases in kidney bean (Phaseolus vulgaris L.) seeds, a cDNA clone (pvss22) for starch synthase II was isolated from developing seeds at the late stage by the combinations of reverse transcriptase-mediated PCR (RT-PCR), 5´-RACE (rapid amplification of cDNA end), and 3´-RACE. The pvss22 cDNA is 2486 bp in length and contains an open reading frame of 738 amino acids. The predicted amino acid sequence of the protein (designated PvSSII-2) encoded by pvss22 cDNA displayed substantial identity (more than 58%) to other dicot starch synthase II members. RNA gel blot analysis revealed that the pvss22 transcripts predominantly accumulate in developing seeds at the middle to late stages. The recombinant PvSSII-2 protein was produced as a major polypeptide in inclusion bodies of Escherichia coli cells. The antiserum raised against proteins extracted from the inclusion bodies recognized at least seven polypeptides in starch-granule fractions from seeds. Analyses of N-terminal sequences of starch-granule-bound proteins showed that three of the seven polypeptides reacting with the antiserum are encoded by the pvss22 gene.
日本応用糖質科学会の論文