Crystal Structure of A-amylose: A Revisit from Synchrotron Microdiffraction Analysis of Single Crystals

Abstract

The three-dimensional structure of A-amylose crystals, as a model of the crystal domains of A-starch granules, was revised using synchrotron radiation microdiffraction data collected from individual micron-sized single crystals. The resulting datasets allowed a determination of the structure with conventional X-ray structure determination techniques normally used for small molecules and not for polymers. Whereas the gross features of this improved structure do not differ extensively from previous structure determination, the high resolution of the diffraction diagrams, which is unusual for a crystalline polymer, allowed the resolution of important new fine details. These include a distortion of the amylose double helices resulting from the occurrence of two intracrystalline molecules of water and a tight network of hydrogen bonds involving each of the primary and secondary hydroxyl groups of the glucosyl moieties. Pairs of water molecules are located in discrete pockets that do not interfere with one another. In addition, the refinement of the new structure indicates a "parallel-down" organization of the amylose molecules within the unit cell as opposed to the previous "parallel-up" model. This new feature indicates that within the crystals, the nonreducing ends of the amylose molecules are oriented toward the c-axis direction of the unit cell. The description of this geometry is important to correlate the crystallography of the granules of A-starch with their ultrastructure and their mode of biosynthesis.Here, we present for the first time the resolution of the structure of a polymer crystal from a full X-ray dataset collected on micron-sized polymer single crystals using synchrotron radiation microdiffraction. This achievement is a substantial advance, which opens the way to many more studies since the technique of growing polymer and biopolymer single crystals is well established.3

A family of starch-active polysaccharide monooxygenases

“…Chitin also contains β(1→4) linkages and has similar crystalline higher order structure to cellulose. (C) Model structure of amylopectin (23)(24)(25). Hydrogen bonds are shown with green dashed lines.…”

“…1C). Double helices can form between amylose and amylopectin in starch, which further complicates the structure (23)(24)(25). Recently, a cellulose-active PMO from N. crassa (22) was found to act on soluble cellodextrins (40) and hemicelluloses that contain β(1→4) linked glucose and glucose derivative units (41).…”

Understanding Starch Structure: Recent Progress

“…Some plants, such as peas and many other legumes, possess granules with a mixed pattern assigned C-type [42,[54][55][56]. In the A-type crystal, the double-helices are closely packed into a monoclinic unit cell (with dimensions a = 20.83 Å, b = 11.45 Å, c = 10.58 Å, space group B2) containing 8 water molecules [57]. In the B-type crystal, the double-helices are packed in a hexagonal unit cell (dimensions a = b = 18.5 Å, c = 10.4 Å, space group P6 1 ) with 36 water molecules [58].…”

Relationship between intrinsic viscosity, thermal and retrogradation properties of amylose and amylopectin

“…Recently, many researchers have reported various properties of amylose such as structural conformation and stability in solvents (Nakanishi et al 1993;Shimada et al 2000;Radosta et al 2001;Tusch et al 2011), conformational transitions (Cheetham & Tao 1997), crystallisation and crystal structure (Takahashi et al 2004;Creek et al 2006;Popov et al 2009;Montesanti et al 2010), amylose complexes (Hulleman et al 1996;Ozcan & Jackson 2002;Nuessli et al 2003;Ciesielski & Tomasik 2004;Cardoso et al 2007;Nishiyama et al 2010), gel microstructure and textural properties (Torres et al 1978;Leloup et al 1992) and amylose gel physical network (Lay & Delmas 1998). Whereas, research on the properties of amylopectin was focused on its structural and retrogradation properties (Manners & Matheson 1981;Manners 1989;Paredes-Lopez et al 1994), crystallinity of amylopectin films and network formation (Putaux et al 2000;Myllarinen et al 2002), and amylopectin complexes (Ciesielski & Tomasik 2004).…”