Starch Technologies, Co., Ltd, Akita Prefectural University, Shimoshinjo-Nakano, Akita-city, Akita, 010-0195, Japan.
Akita Natural Science Laboratory, 25-44 Oiwake-Nishi, Tennoh, Katagami, Akita, 010-0101, Japan.
Plant Mol Biol. 2022 Mar;108(4-5):291-306. doi: 10.1007/s11103-021-01183-3. Epub 2021 Oct 2.
Two opposing models for the amylopectin structure are historically and comprehensively reviewed, which leads us to a better understanding of the specific fine structure of amylopectin. Amylopectin is a highly branched glucan which accounts for approximately 65-85 of starch in most plant tissues. However, its fine structure is still not fully understood due to the limitations of current methodologies. Since the 1940 s, many scientists have attempted to elucidate the distinct structure of amylopectin. One of the most accepted concepts is that amylopectin has a structural element known as "cluster", in which neighboring side chains with a degree of polymerization of ≥ 10 in the region of their non-branched segments form double helices. The double helical structures are arranged in inter- and intra-clusters and are the origin of the distinct physicochemical and crystalline properties of starch granules. Several models of the cluster structure have been proposed by starch scientists worldwide during the progress of analytical methods, whereas no direct evidence so far has been provided. Recently, Bertoft and colleagues proposed a new model designated as "the building block and backbone (BB) model". The BB model sharply contrasts with the cluster model in that the structural element for the BB model is the building block, and that long chains are separately synthesized and positioned from short chains constituting the building block. In the present paper, we conduct the historical review of the cluster concept detailing how and when the concept was established based on experimental results by many scientists. Then, differences between the two opposing concepts are explained and both models are critically discussed, particularly from the point of view of the biochemical regulation of amylopectin biosynthesis.
两种对立的支链淀粉结构模型在历史上得到了全面的回顾，这使我们对支链淀粉的特定精细结构有了更好的理解。支链淀粉是一种高度分支的葡聚糖，约占大多数植物组织中淀粉的 65-85%。然而，由于目前方法的局限性，其精细结构仍未完全了解。自 20 世纪 40 年代以来，许多科学家试图阐明支链淀粉的独特结构。其中最被接受的概念之一是，支链淀粉具有一种称为“簇”的结构单元，其中在其非支化片段区域具有≥10 聚合度的相邻侧链形成双螺旋。双螺旋结构在簇内和簇间排列，是淀粉颗粒独特的物理化学和结晶性质的起源。在分析方法的进展过程中，世界各地的淀粉科学家提出了几种簇结构模型，然而，迄今为止没有提供直接证据。最近，Bertoft 及其同事提出了一种新的模型，称为“构建块和主链（BB）模型”。BB 模型与簇模型形成鲜明对比，因为 BB 模型的结构单元是构建块，而长链是从构成构建块的短链中分别合成和定位的。在本文中，我们对簇概念进行了历史回顾，详细说明了该概念是如何以及何时基于许多科学家的实验结果建立起来的。然后，解释了两种对立概念之间的差异，并对两种模型进行了批判性讨论，特别是从支链淀粉生物合成的生化调控角度进行了讨论。
