Okada Keisuke, Someya Taichi, Osanai Takashi
School of Agriculture, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, Kanagawa, 214-8571, Japan.
Plant Mol Biol. 2025 Jul 31;115(4):99. doi: 10.1007/s11103-025-01623-4.
A storage polysaccharide in the red alga Cyanidioschyzon merolae is semi-amylopectin, a glucan with properties intermediate between noncrystalline glycogen and semicrystalline amylopectin. The debranching enzyme isoamylase plays a crucial role in determining the semicrystalline nature of glucans. In amylopectin-storing organisms, isoamylases consist of the isozymes ISA1, ISA2, and ISA3, with the former two primarily responsible for semicrystallinity. While the semicrystallinity of C. merolae semi-amylopectin is weaker than that of amylopectin, it retains a semicrystalline structure. Based on a previous analysis of isoamylase-deficient strains of C. merolae, the isoform CMI294C is the main contributor to glucan synthesis. Although the biochemical properties of isoamylases involved in amylopectin synthesis have been characterized, those of isoamylases involved in semi-amylopectin synthesis remain largely unknown. Here, we performed a detailed biochemical analysis of CMI294C to gain insights of isoamylases in semi-amylopectin synthesis. Similar to isoamylases in amylopectin-synthesizing organisms, CMI294C hydrolyzes amylopectin more efficiently than glycogen. However, unlike typical isoamylases, CMI294C is uniquely more active against pullulan than against glycogen; and it is strongly inhibited by Zn²⁺. Our results indicate that CMI294C can be potentially used for industrial maltose production due to its enzymatic properties. Overall, our findings provide molecular insights into the isoamylase in glucan structure modulation and enhance our understanding of glucan metabolism in C. merolae.
红藻梅氏嗜热蓝细菌中的一种储存多糖是半支链淀粉，它是一种葡聚糖，其性质介于非结晶性糖原和半结晶性支链淀粉之间。去分支酶异淀粉酶在决定葡聚糖的半结晶性质方面起着关键作用。在储存支链淀粉的生物体中，异淀粉酶由同功酶ISA1、ISA2和ISA3组成，前两者主要负责半结晶性。虽然梅氏嗜热蓝细菌半支链淀粉的半结晶性比支链淀粉弱，但它仍保留着半结晶结构。基于之前对梅氏嗜热蓝细菌异淀粉酶缺陷菌株的分析，异构体CMI294C是葡聚糖合成的主要贡献者。虽然参与支链淀粉合成的异淀粉酶的生化特性已得到表征，但参与半支链淀粉合成的异淀粉酶的生化特性在很大程度上仍不清楚。在此，我们对CMI294C进行了详细的生化分析，以深入了解异淀粉酶在半支链淀粉合成中的作用。与合成支链淀粉的生物体中的异淀粉酶类似，CMI294C水解支链淀粉的效率高于糖原。然而，与典型的异淀粉酶不同，CMI294C对普鲁兰多糖的活性比对糖原的活性更强；并且它受到Zn²⁺的强烈抑制。我们的结果表明，由于其酶学特性，CMI294C有潜力用于工业麦芽糖生产。总体而言，我们的研究结果为葡聚糖结构调控中的异淀粉酶提供了分子层面的见解，并增进了我们对梅氏嗜热蓝细菌中葡聚糖代谢的理解。
