Trapping of a covalent enzyme intermediate in the reaction of Bacillus macerans cyclomaltodextrin glucanyltransferase with cyclomaltohexaose

Contributions of Dexter French (1918-1981) to cycloamylose/cyclodextrin and starch science

Professor Dexter French (1918-1981) was an American chemist and biochemist at Iowa State College (University in 1959). He devoted his career to advance knowledge of polysaccharides and oligosaccharides, in particular starch, cyclodextrins, and enzymes. Cyclodextrins are oligosaccharides obtained from starch and are typically cage molecules with a hydrophobic cavity that can encapsulate other compounds nowadays the basis for many industrial applications. Since the 1960s, he has been recognized as an outstanding authority in the field of starches and cyclodextrins and has inspired researchers in laboratories around the world. This review, on the fortieth anniversary of his death, commemorates his remarkable contribution to starch and cyclodextrin chemistry. Firstly, we give an overview of his personal life and career. Secondly, we highlight some of the results on starch and cyclodextrins from Professor French and his group. A third part discusses his impact on the modern chemistry of cyclodextrins and starch.

Domain characterization of a 4-alpha-glucanotransferase essential for maltose metabolism in photosynthetic leaves

Maltose metabolism during the conversion of transitory (leaf) starch to sucrose requires a 4-alpha-glucanotransferase (EC 2.4.1.25) in the cytosol of leaf cells. This enzyme is called DPE2 because of its similarity to the disproportionating enzyme in plastids (DPE1). DPE1 does not use maltose; it primarily transfers a maltosyl unit from one maltotriose to a second maltotriose to make glucose and maltopentaose. DPE2 is a modular protein consisting of a family 77 glycosyl hydrolase domain, similar to DPE1, but unlike DPE1 the domain is interrupted by an insertion of approximately 150 amino acids as well as an N-terminal extension that consists of two carbohydrate binding modules. Phylogenetic analysis shows that the DPE2-type enzyme is present in a limited but highly diverse group of organisms. Here we show that DPE2 transfers the non-reducing glucosyl unit from maltose to glycogen by a ping-pong mechanism. The forward reaction (consumption of maltose) is specific for the beta-anomer of maltose, while the reverse reaction (production of maltose) is not stereospecific for the acceptor glucose. Additionally, through deletion mutants we show that the glycosyl hydrolase domain alone provides disproportionating activity with a much higher affinity for short maltodextrins than the complete wild-type enzyme, while absence of the carbohydrate binding modules completely abolishes activity with large complex carbohydrates, reflecting the presumed function of DPE2 in vivo.

Formation of covalent β-linked carbohydrate–enzyme intermediates during the reactions catalyzed by α-amylases

Porcine pancreatic and Bacillus amyloliquefaciens alpha-amylases were examined for the formation of covalent carbohydrate intermediates during reaction. The enzymes were precipitated and denatured by adding 10 volumes of acetone. When these denatured enzymes were mixed with methyl alpha-6-[(3)H]-maltooligosaccharide glycosides and chromatographed on BioGel P-2, no carbohydrate was found in the protein void volume peak. When the enzymes were added to the methyl alpha-6-[(3)H]-maltooligosaccharide glycosides and allowed to react for 15s at 1 degrees C and then precipitated and denatured with 10 volumes of acetone, (3)H-labeled carbohydrates were found in the BioGel P-2 protein void volume peak, indicating the formation of enzyme-carbohydrate covalent intermediates. (1)H NMR analysis of the denatured enzyme from the reaction with methyl alpha-maltooligosaccharide glycosides confirmed that carbohydrate was attached to the denatured enzyme. (1)H NMR saturation-transfer analysis further showed that the carbohydrate was attached to the denatured enzyme by a beta-configuration. This configuration is what would be expected for an enzyme that catalyzes the hydrolysis of alpha-(1-->4) glycosidic linkages by a two-step, S(N)2 double-displacement reaction to give retention of the alpha-configuration of the substrates at the reducing-end of the products.

Optimized synthesis of specific sizes of maltodextrin glycosides by the coupling reactions of Bacillus macerans cyclomaltodextrin glucanyltransferase

Bacillus macerans cyclomaltodextrin glucanyltransferase (CGTase, EC 2.4.1.19), in reaction with cyclomaltohexaose and methyl alpha-D-glucopyranoside, methyl beta-D-glucopyranoside, phenyl alpha-D-glucopyranoside, and phenyl beta-D-glucopyranoside gave four kinds of maltodextrin glycosides. The reactions were optimized by using different ratios of the individual d-glucopyranosides to cyclomaltohexaose, from 0.5 to 5.0, to obtain the maximum molar percent yields of products, which were from 68.3% to 78.6%, depending on the particular D-glucopyranoside, and also to obtain different maltodextrin chain lengths. The lower ratios of 0.5-1.0 gave a wide range of sizes from d.p. 2-17 and higher. As the molar ratio was increased from 1.0 to 3.0, the larger sizes, d.p. 9-17, decreased, and the small and intermediate sizes, d.p. 2-8, increased; as the molar ratios were increased further from 3.0 to 5.0, the large sizes completely disappeared, the intermediate sizes, d.p. 4-8, decreased, and the small sizes, d.p. 2 and 3 became predominant. A comparison is made with the synthesis of maltodextrins by the reaction of CGTase with different molar ratios of d-glucose to cyclomaltohexaose.

Enzymatic synthesis of two salicin analogues by reaction of salicyl alcohol with Bacillus macerans cyclomaltodextrin glucanyltransferase and Leuconostoc mesenteroides B-742CB dextransucrase

Beta-Salicin is a naturally occurring glycoside found in the bark of poplar and willow trees. Ancient man used it as an analgesic and antipyretic. It has a D-glucopyranose unit attached by a beta-linkage to the phenolic hydroxyl of salicyl alcohol. Two new salicin analogues have been enzymatically synthesized by transglycosylation reactions: (a) by the reaction of Bacillus macerans cyclomaltodextrin glucanyltransferase with cyclomaltohexaose and salicyl alcohol, followed by reactions with alpha amylase and glucoamylase to give D-glucopyranose attached by an alpha-linkage to the phenolic hydroxyl of salicyl alcohol as the major product, alpha-salicin; and (b) by the reaction of Leuconostoc mesenteroides B-742CB dextransucrase with sucrose and salicyl alcohol, followed by reactions with dextranase and glucoamylase to give alpha-d-glucopyranose attached to the primary alcohol hydroxyl of salicyl alcohol as the major product, alpha-isosalicin.

Bacillus macerans cyclomaltodextrin glucanotransferase transglycosylation reactions with different molar ratios of D-glucose and cyclomaltohexaose

It was found that Bacillus macerans cyclomaltodextrin glucanotransferase (CGTase) reacts with cyclomaltohexaose (alpha-cyclodextrin, alpha-CD) to give a series of cyclomaltooligosaccharides (cyclomaltodextrins, CDs), having seven to more than 20 D-glucose residues and maltooligosaccharides (maltodextrins, MDs) from G5 to G12+. When D-glucose (Glc) was added to the alpha-CD at very low molar ratios (1:100) of Glc to alpha-CD, the predominant products (95%) were CDs, some of which were macrocyclic MDs with 20-60 D-glucose residues, along with MDs that also had high molecular weights, containing 10-75 D-glucose residues and gave a blue iodine-iodide color. As the molar ratio of Glc to alpha-CD was increased, the amount of CDs progressively decreased and MDs proportionately increased in the range of G2-G12. At 25 mM alpha-CD and Glc to alpha-CD molar ratio of 1:1, a 75% yield of MDs, G1-G12, each in approximately equal amounts, was obtained; and at 20 mM and a 5:1 ratio, a 97% yield of MDs, G2-G9, was obtained but in unequal amounts. At higher ratios (10:1), the CDs completely disappeared, and at very high ratios (50:1 to 100:1) only low-molecular-weight MDs, G2-G4, were formed.

Addition of maltodextrins to the nonreducing-end of acarbose by reaction of acarbose with cyclomaltohexaose and cyclomaltodextrin glucanyltransferase

New kinds of acarbose analogues were synthesized by the reaction of acarbose with cyclomaltohexaose and cyclomaltodextrin glucanyltransferase (CGTase). Three major CGTase coupling products were separated and purified by Bio-Gel P2 gel-permeation chromatography. Digestion of the three products by beta-amylase and glucoamylase showed that they were composed of maltohexaose (G6), maltododecaose (G12), and maltooctadecaose (G18), respectively, attached to the nonreducing-end of acarbose. 13C NMR of the glucoamylase product (D-glucopyranosyl-acarbose) showed that the D-glucose moiety was attached alpha- to the C-4-OH group of the nonreducing-end cyclohexene ring of acarbose, indicating that the maltodextrins were attached alpha-(1-->4) to the nonreducing-end cyclohexene of acarbose.