The fine structure of cassava starch amylopectin. Part 2: Building block structure of clusters

Understanding Starch Structure: Recent Progress

“…In all samples analysed so far, group 2 building blocks predominate in the clusters: roughly 40-65% of all building blocks (on a number basis) have only two chains. The abundance then decreases with increasing number of chains, so that group 6 only represents a few per cent or less of the blocks, and the size-distribution is surprisingly similar regardless the structural type of amylopectin (Table 3) [191,211,223,[229][230][231][232][234][235][236][237]. It is noted that the largest building blocks in group 6 contains as many chains as is found in a large part of the clusters.…”

“…Nevertheless, the concept of building blocks can be rationalised to consist of diverse groups of α-LDs with increasing number of chains. Thus, group 2 consists of building blocks with two chains and have DP 5-9, group 3 have three chains (DP 10-14) and group 4 have four chains (DP [15][16][17][18][19] [231][232][233]. As the complexity of each group increases with the size, the larger building blocks have only been isolated as course preparations.…”

“…Therefore, it is most unlikely that L-chains penetrating the crystalline lamella as radially organised double-helices also extend through the amorphous lamella as helices and in the same radial direction. Bertoft and co-workers [225,229,230,232] found that the structure of the multiply branched dextrins produced by α-amylase from B. amyloliquefaciens does not conform to the expected structure of clusters proposed in the cluster model. The model predicts that isolated clusters only contain short chains, because the long chains have to be cleaved in order to release the clusters from the macromolecule.…”

“…In contrast to the cluster model, however, the backbone is (more or less) completely embedded in the amorphous lamella and extends along it, rather than traversing the stacks of lamellae in the semi-crystalline "growth ring". The building blocks are separated by inter-block segments (DP 5-8 depending on starch source, Table 3) and occasionally these segments are slightly longer, forming the inter-cluster segments that the α-amylase of B. amyloliquefaciens readily attacks at initial stages of hydrolysis [225,232]. It is apparent, however, that the actual function of the inter-cluster segments is the same as that of the inter-block segments; they interconnect building blocks.…”

Characterization of Function of the GlgA2 Glycogen/Starch Synthase in Cyanobacterium sp. Clg1 Highlights Convergent Evolution of Glycogen Metabolism into Starch Granule Aggregation

“…The minor fraction, amylose, is composed of linear weakly branched glucan chains (less than 1% of a-1,6 branches), while the major fraction, amylopectin, harbors an ordered branch pattern of a-1,6 linkages, leading to the cluster organization responsible for starch crystallinity (Hizukuri, 1986;Bertoft et al, 2010;Laohaphatanaleart et al, 2010). The synthesis of starch granules was initially believed to be a hallmark of three sister lineages, plants/green algae, red algae, and glaucophytes (i.e.…”