Marine Bioengineering Group, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China; University of Chinese Academy of Sciences, Beijing 100039, China.
Department of Pharmaceutical & Biological Engineering, School of Chemical Engineering, Sichuan University, Chengdu, Sichuan 610065, China.
J Plant Physiol. 2017 Nov;218:84-93. doi: 10.1016/j.jplph.2017.07.019. Epub 2017 Jul 28.
In a marine green starch-producing microalga Tetraselmis subcordiformis, the role of starch phosphorylase (SP) in the starch biosynthesis was disclosed by characterizing the enzyme properties and activity variations during the starch accumulation process. TsSP4, a SP isoform accounting for the major SP activity in T. subcordiformis, was unique to be active in a monomer form with a molecular weight of approximately 110kDa. It resembled one of the chloroplast-located SPs (PhoA) in Chlamydomonas reinhardtii with a similarity of 63.3% in sequence, though it possessed the typical L78/80 domain found in the plastidial SPs (Pho1) of higher plants that was absent in PhoA. TsSP4 exhibited moderate sensitivity to ADP-Glc inhibition and had a high activity for longer-chain linear maltooligosacchride (MOS) and amylopectin against highly branched glycogen as the substrates. TsSP4 had 2-fold higher affinity for Glc-1-P in the synthetic direction than for Pi in the phosphorolytic direction, and the catalytic constant k for Glc-1-P was 2-fold of that for Pi. Collectively, TsSP4 preferred synthetic rather than phosphorolytic direction. TsSP4 could elongate MOSs even initially with Pi alone in the absence of Glc-1-P, which further supported its synthetic role in the starch biosynthesis. TsSP4 displayed increased activities in the developing and mature stage of starch biosynthesis under nitrogen-starvation conditions, indicating its possible contribution to the amylopectin amplification.
在海洋绿色产淀粉微藻塔胞藻中，通过研究淀粉合成过程中酶特性和活性变化，揭示了淀粉磷酸化酶（SP）在淀粉生物合成中的作用。TsSP4 是塔胞藻中主要的 SP 同工酶之一，以单体形式存在，分子量约为 110kDa，具有独特的活性。它与衣藻（Chlamydomonas reinhardtii）中的一种质体定位的 SP（PhoA）在序列上具有 63.3%的相似性，尽管它具有高等植物质体定位的 SP（Pho1）中典型的 L78/80 结构域，而 PhoA 中则没有。TsSP4 对 ADP-Glc 抑制具有中等敏感性，对长链线性麦芽寡糖（MOS）和支链淀粉（amylopectin）的活性较高，而对高度分支的糖原（glycogen）的活性较低。TsSP4 在合成方向上对 Glc-1-P 的亲和力是对 Pi 的两倍，催化常数 k 对 Glc-1-P 是对 Pi 的两倍。总的来说，TsSP4 更倾向于合成方向，而不是磷酸化方向。TsSP4 可以在没有 Glc-1-P 的情况下仅用 Pi 延长 MOS，这进一步支持了它在淀粉生物合成中的合成作用。TsSP4 在氮饥饿条件下淀粉生物合成的发育和成熟阶段的活性增加，表明它可能对支链淀粉的扩增有贡献。
