Starch, the most abundant carbohydrate reserve in plants, primarily consists of the branched glucan amylopectin, which forms semi-crystalline granules. Phase transition from a soluble to an insoluble form depends on amylopectin architecture, requiring a compatible distribution of glucan chain lengths and a branch-point distribution. Here, we show that two starch-bound proteins, LIKE EARLY STARVATION 1 (LESV) and EARLY STARVATION 1 (ESV1), which have unusual carbohydrate-binding surfaces, promote the phase transition of amylopectin-like glucans, both in a heterologous yeast system expressing the starch biosynthetic machinery and in Arabidopsis plants. We propose a model wherein LESV serves as a nucleating role, with its carbohydrate-binding surfaces helping align glucan double helices to promote their phase transition into semi-crystalline lamellae, which are then stabilized by ESV1. Because both proteins are widely conserved, we suggest that protein-facilitated glucan crystallization may be a general and previously unrecognized feature of starch biosynthesis.

中文翻译：

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LIKE EARLY STARVATION 1和EARLY STARVATION 1促进和稳定淀粉生物合成中的支链淀粉相变

淀粉是植物中最丰富的碳水化合物储备，主要由形成半结晶颗粒的支链葡聚糖支链淀粉组成。从可溶形式到不溶形式的相变取决于支链淀粉结构，需要葡聚糖链长度的相容分布和分支点分布。在这里，我们展示了两种淀粉结合蛋白，如 EARLY STARVATION 1 (LESV) 和 EARLY STARVATION 1 (ESV1)，它们具有不寻常的碳水化合物结合表面，促进支链淀粉样葡聚糖的相变，两者均在异源酵母系统中表达淀粉生物合成机制并在拟南芥植物。我们提出了一个模型，其中 LESV 充当成核作用，其碳水化合物结合表面有助于对齐葡聚糖双螺旋，以促进它们相变为半结晶薄片，然后由 ESV1 稳定。因为这两种蛋白质都广泛保守，我们认为蛋白质促进的葡聚糖结晶可能是淀粉生物合成的普遍且以前未被认识的特征。