Amylose is a linear polymer chain of α-d-glucose units connected through α(1 → 4) glycosidic bonds. Experimental studies show that in non-polar solvents, single amylose chains form helical structures containing precise H-bond patterns. However, both experimental and computational studies indicate that these perfectly H-bonded helices are not stable in pure water. Nevertheless, amylose chains are observed to form helix-like structures in molecular dynamics (MD) simulations that exhibit imperfect H-bond patterns. In this paper, we study the structure of amylose chains in water using MD simulations to identify and characterize these “imperfect” helical structures. To this end we devise geometry-based criteria to define imperfect helical structures in amylose chains. Using this approach, the propensity of amylose chains to form these structures is quantified as a function of chain length and solvent temperature. This analysis also uncovers both short and long time helix-breaking mechanisms such as band-flips and kinks in the chain. This geometric approach to defining imperfect helices thus allows us to give new insight into the secondary structure of single amylose chains in spite of imperfect H-bond patterns.

Bacteria have acquired sophisticated mechanisms for assembling and disassembling polysaccharides of different chemistry. α-d-Glucose homopolysaccharides, so-called α-glucans, are the most widespread polymers in nature being key components of microorganisms. Glycogen functions as an intracellular energy storage while some bacteria also produce extracellular assorted α-glucans. The classical bacterial glycogen metabolic pathway comprises the action of ADP-glucose pyrophosphorylase and glycogen synthase, whereas extracellular α-glucans are mostly related to peripheral enzymes dependent on sucrose. An alternative pathway of glycogen biosynthesis, operating via a maltose 1-phosphate polymerizing enzyme, displays an essential wiring with the trehalose metabolism to interconvert disaccharides into polysaccharides. Furthermore, some bacteria show a connection of intracellular glycogen metabolism with the genesis of extracellular capsular α-glucans, revealing a relationship between the storage and structural function of these compounds. Altogether, the current picture shows that bacteria have evolved an intricate α-glucan metabolism that ultimately relies on the evolution of a specific enzymatic machinery. The structural landscape of these enzymes exposes a limited number of core catalytic folds handling many different chemical reactions. In this Review, we present a rationale to explain how the chemical diversity of α-glucans emerged from these systems, highlighting the underlying structural evolution of the enzymes driving α-glucan bacterial metabolism.

The helical structure of V‐amylose offering a superior encapsulation affinity compared with the other polysaccharides, especially toward the amphiphilic or hydrophobic molecules; in addition to providing a higher resistance toward enzymatic hydrolysis support its applications as a potential drug delivery vehicle. Mainly, the glycosidic linkages and –CH2– groups forming the hydrophobic cavity of V‐amylose helix, and the glycosyl hydroxyl groups constituting its hydrophilic periphery promote the loading of a diverse range of molecules via van der Waals forces and hydrogen bonding interactions. These properties enable a high‐loading efficiency, targeted delivery, and controlled release of the cargo drug molecules by V‐amylose. Besides, V‐amylose presents characteristics of an ideal drug delivery system, such as biocompatibility, physiological benevolence, nonimmunogenicity, and biodegradability. The V‐amylose polysaccharide chains fold into left‐handed single helix comprising of six glucose units in each turn having a pitch height of 7.91–8.17 Å. These structural features of V‐amylose differentiate it from the parent amylose polysaccharide and enable the accommodation and nanoencapsulation of a wide range of therapeutics in the former. The tightly packed helical structure of V‐amylose provides extraordinary resistance toward digestion by amylase compared with the linear polysaccharides, which supports the application of V‐amylose as controlled drug release systems. The activity of the amylase enzyme produced by salivary glands, pancreas, gastrointestinal tract, and gut microbiota on amylose‐based drug delivery vehicles promote enzyme‐sensitive controlled oral and colon‐specific release of the encapsulated drug. The single helical V‐amylose with hydrophobic core and hydrophilic periphery forms inclusion complexes that improve the absorption and permeation of drugs having a high clogP index. The present commentary highlights the distinguished features of V‐amylose as an imminent drug delivery system.

By the end of this section, you will be able to: Carbohydrates provide energy for the cell and structural support to plants, fungi, and arthropods such as insects, spiders, and crustaceans. Consisting of carbon, hydrogen, and oxygen in the ratio CH2O or carbon hydrated with water, carbohydrates are classified as monosaccharides, disaccharides, and polysaccharides depending on the number of monomers in the macromolecule. Monosaccharides are linked by glycosidic bonds that form as a result of dehydration synthesis. Glucose, galactose, and fructose are common isomeric monosaccharides, whereas sucrose or table sugar is a disaccharide. Examples of polysaccharides include cellulose and starch in plants and glycogen in animals. Although storing glucose in the form of polymers like starch or glycogen makes it less accessible for metabolism, this prevents it from leaking out of cells or creating a high osmotic pressure that could cause excessive water uptake by the cell. Insects have a hard outer skeleton made of chitin, a unique nitrogen-containing polysaccharide.

How pyridoxal 5'-phosphate could function in glycogen phosphorylase catalysis. A mechanism for the phosphorylase reaction is proposed which offers a plausible explanation for the essential role of pyridoxal 5'-phosphate in glycogen phosphorylases: in the forward direction, phosphorolysis of alpha-1,4-glycosidic bonds in oligo- or polysaccharides is started by protonation of the glycosidic oxygen by the substrate orthophosphate followed by stabilization of the incipient oxocarbonium ion and subsequent covalent binding to form alpha-glucose 1-phosphate. In the reverse direction, protonation of the phosphate of glucose 1-phosphate destabilizes the glycosidic bond and promotes formation of a glucosyl oxocarbonium ion-phosphate anion pair. In the subsequent step the phosphate anion facilitates the nucleophilic attack of a terminal glucosyl residue on the carbonium ion bringing about alpha-1,4-glycosidic bond formation and primer elongation. Both in the forward and reverse reactions, the phosphate of the cofactor pyridoxal 5'-phosphate acts as a general acid (PL-OPO3H- or PL-OPO3(2-) and protonates the substrate phosphate functioning as proton shuttle.

The N-terminal starch binding domain of Rhizopus oryzae glucoamylase (RoSBD) has a high binding affinity for raw starch. RoSBD has two ligand-binding sites, each containing a ligand-binding clamp: a polyN clamp residing near binding site I is unique in that it is expressed in only three members of carbohydrate binding module family 21 (CBM21) members, and a Y32/F58 clamp located at binding site II is conserved in several CBMs. Here we characterized different roles of these sites in the binding of insoluble and soluble starches using an amylose-iodine complex assay, atomic force microscopy, iso