Structural Characterization of Glucooligosaccharide Oxidase from Acremonium strictum

Abstract

Glucooligosaccharide oxidase from Acremonium strictum was screened for potential applications in oligosaccharide acid production and carbohydrate detection. This protein is a unique covalent flavoenzyme which catalyzes the oxidation of a variety of carbohydrates with high selectivity for cello-and maltooligosaccharides. Kinetic measurements suggested that this enzyme possesses an open carbohydrate-binding groove, which is mainly composed of two glucosyl-binding subsites. The encoding gene was subsequently cloned, and one intron was detected in the genomic DNA. Large amounts of active enzymes were expressed in Pichia pastoris, with a yield of 300 mg per liter medium. The protein was predicted to share structural homology with plant cytokinin dehydrogenase and related flavoproteins that share a conserved flavin adenine dinucleotide (FAD)-binding domain. The closest sequence matches are those of plant berberine bridge enzyme-like proteins, particularly the characteristic flavinylation site. Unexpectedly, mutation of the putative FAD-attaching residue, H70, to alanine, serine, cysteine, and tyrosine did not abolish the covalent FAD linkage and had little effect on the K m . Instead, the variants displayed k cat values that were 50-to 600-fold lower, indicating that H70 is crucial for efficient redox catalysis, perhaps through modulation of the oxidative power of the flavin.Sugar oxidases and dehydrogenases that catalyze the oxidation of glucose and other carbohydrates into the corresponding lactones are widely distributed in nature. These enzymes have received great attention as potential diagnostic reagents and industrial biocatalysts. For example, glucose oxidase (GOX) is widely used in analytical biochemistry and in the food industry (21,22). A search of the BRENDA enzyme database (23) revealed that most of these enzymes are specific for a variety of mono-and disaccharides, and only a few enzymes exhibit high specificity with oligosaccharides. The latter enzymes include galactose oxidase, cellobiose dehydrogenase (CDH), and glucooligosaccharide oxidase (GOOX). GOOX from Acremonium strictum was identified from sugar oxidase-producing microorganisms with the aim of identifying enzymes with potential applications in oligosaccharide acid production and alternative carbohydrate assays (16).GOOX is a monomeric glycoprotein with a covalently linked flavin adenine dinucleotide (FAD) (16). It catalyzes the oxidization of a variety of carbohydrates with concomitant reduction of molecular oxygen to hydrogen peroxide. Screening of 30 monosaccharides and derivatives of these compounds showed that D-glucose is the only good substrate. In terms of the disaccharides, maltose, cellobiose, and lactose with reducing-end glucosyl residues linked by an ␣ bond or ␤-1,4 bonds are good substrates, whereas disaccharides containing other linkage types are not. Moreover, GOOX can react with maltooligosaccharides composed of ␣-1,4-linked D-glucopyranosyl residues (up to at least seven units); hence, the name of this novel oxidase. The broad...

6-S-Cysteinylation of Bi-covalently Attached FAD in Berberine Bridge Enzyme Tunes the Redox Potential for Optimal Activity

“…In the case of glucooligosaccharide oxidase it is reported that replacement of His by various amino acids resulted in the isolation of proteins still bearing a covalently linked cofactor via the second site of attachment. However, not much information regarding the expression level and the spectral properties of these muteins was presented in these reports (5,6). For hexose oxidase from Chondrus crispus, which has been shown to be a bi-covalently flavinylated enzyme, spectral data indicative for the presence of a retained 6-S-cysteinyl linkage when replacing His with another amino acid are reported; however, the expression level is reduced from 3 g to ϳ50 mg for this mutein (6).…”

“…Recently, we have developed an expression system in Pichia pastoris that enabled us to obtain sufficient quantities of purified BBE from Eschscholzia californica, allowing a more detailed characterization. In the course of these studies it was discovered that BBE belongs to a novel group of flavoproteins containing a bi-covalently attached flavin cofactor (3)(4)(5)(6)(7).…”

Production of Calcium Lactobionate by a Lactose-oxidizing Enzyme from <i>Paraconiothyrium</i> sp. KD-3

“…The Paraconiothyrium enzyme lacking heme in the protein is discriminated from CDH, 7,8) which contains heme. CBQ, 9,10) GOOX 11,12) and COX, 13) however, have similar properties; for instance, a molecular mass of 55 60 kDa, a broad substrate specificity, and the presence of FAD as a prothetic group. On the other hand, CDH and CBQ have similar amino acid sequences.…”

“…Some enzymes have been known to oxidize lactose. Such enzymes, cellobiose dehydrogenases (EC 1.1.99.18, CDH), 7,8) cellobiose: quinone oxidoreductases (EC 1.1.5.1, CBQ), 9,10) glucooligosaccharides oxidases (GOOX), 11,12) and carbohydrate: acceptor oxidoreductase (COX), 13) however, have not been studied from a viewpoint of calcium lactobionate production in detail. This may be due to their instability at acidic pH, and or low specificity on O2 as an electron acceptor.…”

Lactobionic and cellobionic acid production profiles of the resting cells of acetic acid bacteria

“…2) Biological methods using bacteria [3][4][5][6][7][8] and fungi [9][10][11][12][13] have also been studied to produce LacA. However, these microorganisms have also not been applied for the production of LacA for foods, because they are not entirely suitable for industrial production from the perspective of food safety.…”