Cycloamyloses are cyclic α-1,4 linked

glucan A glucan is a polysaccharide derived from D-glucose, linked by glycosidic bonds. Glucans are noted in two forms: alpha glucans and beta glucans. Many beta-glucans are medically important. They represent a drug target for antifungal medications of ...

s comprising dozens or hundreds of

glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...

units. Chemically they are similar to the much smaller

cyclodextrin Cyclodextrins are a family of cyclic oligosaccharides, consisting of a macrocycle, macrocyclic ring of glucose subunits joined by α-1,4 glycosidic bonds. Cyclodextrins are produced from starch by enzyme, enzymatic conversion. They are used in ...

s, which are typically composed of 6, 7 or 8 glucose units. Animated Amylose

Discovery

Cycloamyloses were discovered as a result of studies of the function of 4-α-glucanotransferase, also known as disproportionating enzyme or D-enzyme (EC 2.4.1.25) isolated from potato.

Synthesis

Upon incubation of D-enzyme with high molecular weight

amylose Amylose is a polysaccharide made of α-D-glucose units, bonded to each other through α(1→4) glycosidic bonds. It is one of the two components of starch, making up approximately 20–25% of it. Because of its tightly packed Helix, helical struct ...

, a product was obtained with decreased ability to form a blue complex with iodine, without reducing or non-reducing ends, and resistant to hydrolysis by glucoamylase (an exoamylase). Takaha and Smith deduced that the product was a cyclic polymer, which they confirmed by mass spectrometry and acid hydrolysis, and showed that it comprised between 17 and several hundred glucose units. It was subsequently shown that D-enzyme could create complex cycloglucans from amylopectin. Similar 4-α-glucanotransferases from bacteria and other organisms have also been shown to produce cycloglucans upon incubation with amylose or amylopectin.

Structure

While the structures of cyclodextrins are planar circles, the structure of cycloamyloses with 10 to 14 glucose units were determined to be circular with strain-induced band-flips and kinks. In contrast the structure of a larger cycloamylose with 26 glucose units was determined to comprise two short left-handed V-amylose helices in antiparallel arrangement.

Applications

Cycloamyloses contain cavities in the helices which are capable of accommodating guest molecules, which suggested applications in chemical technologies. Cycloamylose is used in artificial chaperone technology for the refolding of denatured proteins. Cycloglucans have physicochemical properties that make them useful in food and manufacturing.

References

{{reflist Polysaccharides Starch Macrocycles