Can cyclodextrin glycosyltransferase be useful for the investigation of the fine structure of amylopectins?: Characterisation of highly branched clusters isolated from digests with potato and maize starches

Understanding Starch Structure: Recent Progress

Starch is a major food supply for humanity. It is produced in seeds, rhizomes, roots and tubers in the form of semi-crystalline granules with unique properties for each plant. Though the size and morphology of the granules is specific for each plant species, their internal structures have remarkably similar architecture, consisting of growth rings, blocklets, and crystalline and amorphous lamellae. The basic components of starch granules are two polyglucans, namely amylose and amylopectin. The molecular structure of amylose is comparatively simple as it consists of glucose residues connected through α-(1,4)-linkages to long chains with a few α-(1,6)-branches. Amylopectin, which is the major component, has the same basic structure, but it has considerably shorter chains and a lot of α-(1,6)-branches. This results in a very complex, three-dimensional structure, the nature of which remains uncertain. Several models of the amylopectin structure have been suggested through the years, and in this review two models are described, namely the “cluster model” and the “building block backbone model”. The structure of the starch granules is discussed in light of both models.

Characterization and Application of BiLA, a Psychrophilic α-Amylase from Bifidobacterium longum

In this study, a novel α-amylase was cloned from Bifidobacterium longum and named BiLA. The enzyme exhibited optimal activity at 20 °C and a pH value of 5.0. Kinetic analysis using various carbohydrate substrates revealed that BiLA had the highest k(cat/)K(m) value for amylose. Interestingly, analysis of the enzymatic reaction products demonstrated that BiLA specifically catalyzed the hydrolysis of oligosaccharides and starches up to G5 from the nonreducing ends. To determine whether BiLA can be used to generate slowly digestible starch (SDS), starch was treated with BiLA, and the kinetic parameters were analyzed using porcine pancreatic α-amylase (PPA) and amyloglucosidase (AMG). Compared to normal starch, BiLA-treated starch showed lower k(cat)/K(m) values with PPA and AMG, suggesting that BiLA is a potential candidate for the production of SDS.

Structures of the amylopectins of waxy, normal, amylose-extender, and wx:ae genotypes and of the phytoglycogen of maize

Average chain lengths and beta-amylolysis limits have been determined for the waxy and ae/wx genotypes of mature maize starch, and for the amylopectin fractions of normal and amylose-extender starches (prepared by precipitation with concanavalin A), rabbit-liver glycogen, phytoglycogen, and waxy rice starch. All amylopectin samples had similar A:B chain ratios of > 1 and the two glycogens had ratios of < 1. This finding led to average frequencies of substitution of B chains over the whole molecule of > 2 for the amylopectins and < 2 for the glycogens. An equation for the number of tiers for a molecule with various frequencies of substitution of B chains and chain lengths has been used to determine the effect of variation in average frequency of branching and average chain length on structure.

Branched saccharides formed by the action of His-modified cyclodextrin glycosyltransferase from Klebsiella pneumoniae M 5 al on starch

Digestion of potato starch with His-modified alpha-cyclodextrin glycosyltransferase from Klebsiella pneumoniae M 5 al yielded branched tetra- to nona-saccharides, as revealed by debranching with pullulanase. Maltose and maltotriose stubs preponderated together with small proportions of D-glucose stubs. The branched saccharides accounted for approximately 1.2% of the starch.

Structural studies of amyloglucan and a soluble glucan produced from starch by Streptococcus sanguis 1 MC 204

Two alpha-D-glucans, produced from amylopectin by an oral isolate Streptococcus sanguis 1 MC 204, were shown to contain both (1----4) and (1----6) linkages. The first alpha-D-glucan (amyloglucan) was adherent and highly insoluble, and methylation analysis, i.r. spectroscopy, and enzymic analyses showed it to be similar to amylopectin but less branched with longer interior and exterior chains. The second polymer was a non-adherent soluble alpha-D-glucan that was similar to amyloglucan but with long exterior chains. These alpha-D-glucans were not synthesised de novo, but were the products of the modification of amylopectin.

Investigation of the fine structure of alpha-dextrins derived from amylopectin and their relation to the structure of waxy-maize starch

Alpha-dextrins, obtained by fractional precipitation with methanol of the products of the action of Bacillus subtilis alpha-amylase on waxy-maize amylopectin, were debranched with isoamylase and the distributions of the unit chains were analysed by gel-permeation chromatography. The large alpha-dextrins still contained long B-chains after hydrolysis for 60 min, but these were absent from the small dextrins with chain numbers of approximately 11 or less. The small dextrins contained increased amounts of chains with lengths intermediate of those of the long B-chains and the main part of the short chains. After hydrolysis for 210 min, almost all of the long B-chains had disappeared and the chains with intermediate lengths had been shortened further. The distributions of the unit chains of the internal chains, obtained by debranching of the phosphorolysis (phi)-limit dextrins, gave similar results and showed that the ratio of A- to B-chains was unchanged during the alpha-amylolysis. Models for the fine structure of the intermediate alpha-dextrins are proposed.

Studies of the inhibition by malto-oligosaccharides of the cyclisation reaction catalysed by the cyclodextrin glycosyltransferase from Klebsiella pneumoniae M 5 al with glycogen

The substrate qualities of malto-oligosaccharides for the disproportionation reaction catalysed by the cyclodextrin glycosyltransferase [(1----4)-alpha-D-glucan:[(1----4)-alpha-D-glucopyranosyl]transferase (cyclising) EC 2.4.1.19] from Klebsiella pneumoniae M 5 al have been re-investigated. Maltose failed to be homologised with measurable velocity. The initial rates of disproportionation and the affinities of the enzyme increased with the chain lengths of the substrates. Maltopentaose was the smallest saccharide which, by disproportionation, yielded longer chains being cyclised initially. D-Glucose did not affect the initial cyclisation from glycogen, but served as acceptor for the "chain-shortening" reaction. Maltose inhibited the initial cyclisation reaction in a linearly competitive manner. Maltotriose and maltotetraose inhibited the cyclisation reaction competitively, the inhibition kinetics pointing to the binding of two effector-molecules to the enzyme. Competitive inhibition was also found with malto-pentaose, -hexaose, and -heptaose. The degrees of inhibition increased from maltose to maltotetraose, and decreased with the larger saccharides; maltotriose and maltotetraose were the most effective inhibitors of the initial cyclisation. Some possibilities for the subsite-mechanisms are discussed.

Cyclodextrin glycosyltransferases from Klebsiella pneumoniae M 5 al and Bacillus macerans: quantitative analysis by high-performance liquid chromatography of the (1 leads to 4)-alpha-D-glucopyranosyl transfer-products from some linear and cyclic substrates

The analysis of the (1 leads to 4)-alpha-D-glucopyranosyl transfer-products from some linear and cyclic substrates by quantitative h.p.l.c. illuminated the mode of action of the cyclodextrin glycosyltransferases [1 leads to 4)-alpha-D-glucan:[(1 leads to 4)-alpha-D-glucopyranosyl]transferase (cyclising), EC 2.4.1.19) from Klebsiella pneumoniae M 5 al and Bacillus macerans. D-Glucopyranosyl transfer, obligatory for maltose (poor substrate), was preferred for maltotriose (good substrate). The lengths of linear disproportionation-products increased with the lengths of the linear substrates. Cyclodextrins were produced from maltotriose and maltopentaose, but not from maltose. The cyclodextrins were substrates in the absence of acceptors. The cyclodextrin transformation started without the formation of detectable amounts of linear transfer-products. The cyclodextrin composition of long-term digests was nearly the same with all the cyclic substrates, cycloheptaamylose being the main cyclic compound. The linear carbohydrate was uniformly distributed from maltose up to at least maltononaose. The enzyme from Bacillus macerans was the least active, but long-term digests yielded results comparable to those obtained with the enzyme from Klebsiella pneumoniae M 5 al.