Biomedical subjects

K H Kalk

Publications and source records attributed to K H Kalk.

At least 37 records · Page 2Linked to original sources

PubMed1998

The three-dimensional structure of the nitrogen regulatory protein IIANtr from Escherichia coli.

The bacterial rpoN operon codes for sigma 54, which is the key sigma factor that, under nitrogen starvation conditions, activates the transcription of genes needed to assimilate ammonia and glutamate. The rpoN operon contains several other open reading frames that are cotranscribed with sigma 54. The product of one of these, the 17.9 kDa protein IIANtr, is homologous to IIA proteins of the phosphoenolpyruvate:sugar phosphotransferase (PTS) system. IIANtr influences the transcription of sigma 54-dependent genes through an unknown mechanism and may thereby provide a regulatory link between carbon and nitrogen metabolism. Here we describe the 2.35 A X-ray structure of Escherichia coli IIANtr. It is the first structure of a IIA enzyme from the fructose-mannitol family of the PTS. The enzyme displays a novel fold characterized by a central mixed parallel/anti-parallel beta-sheet surrounded by six alpha-helices. The active site His73 is situated in a shallow depression on the protein surface.

Amino Acid Sequence↗

PubMed1998

The structure of the Escherichia coli phosphotransferase IIAmannitol reveals a novel fold with two conformations of the active site.

BACKGROUND: The bacterial phosphoenolpyruvate-dependent phosphotransferase system (PTS) catalyses the cellular uptake and subsequent phosphorylation of carbohydrates. Moreover, the PTS plays a crucial role in the global regulation of various metabolic pathways. The PTS consists of two general proteins, enzyme I and the histidine-containing protein (HPr), and the carbohydrate-specific enzyme II (EII). EIIs are usually composed of two cytoplasmic domains, IIA and IIB, and a transmembrane domain, IIC. The IIA domains catalyse the transfer of a phosphoryl group from HPr to IIB, which phosphorylates the transported carbohydrate. Knowledge of the structures of the IIA proteins may provide insight into the mechanisms by which the PTS couples phosphorylation reactions with carbohydrate specificity. RESULTS: We have determined the crystal structure of the Escherichia coli mannitol-specific IIA domain, IIAmtl (M(r) 16.3 kDa), by multiple anomalous dispersion analysis of a selenomethionine variant of IIAmtl. The structure was refined at 1.8 A resolution to an R factor of 19.0% (Rfree 24.2%). The enzyme consists of a single five-stranded mixed beta sheet, flanked by helices on both sides. The phosphorylation site (His65) is located at the end of the third beta strand, in a shallow crevice lined with hydrophobic residues. The sidechains of two conserved active-site residues, Arg49 and His111, adopt two different conformations in the four independent IIAmtl molecules. Using a solution structure of phosphorylated HPr, and a combination of molecular modelling and NMR binding experiments, structural models of the HPr-IIAmtl complex were generated. CONCLUSIONS: The fold of IIAmtl is completely different from the structures of other IIA proteins determined so far. The two conformations of Arg49 and His111 might represent different states of the active site, required for the different phosphoryl transfer reactions in which IIAmtl is involved. A comparison of the HPr-IIAmtl model with models of HPr in complex with other IIA enzymes shows that the overall interaction mode between the two proteins is similar. Differences in the stabilisation of the invariant residue Arg17 of HPr by the different IIA proteins might be part of a subtle mechanism to control the hierarchy of carbohydrate utilisation by the bacterium.

Bacterial Proteins↗

PubMed1998

Crystal structure of a murine alpha-class glutathione S-transferase involved in cellular defense against oxidative stress.

Glutathione S-transferases (GSTs) are ubiquitous multifunctional enzymes which play a key role in cellular detoxification. The enzymes protect the cells against toxicants by conjugating them to glutathione. Recently, a novel subgroup of alpha-class GSTs has been identified with altered substrate specificity which is particularly important for cellular defense against oxidative stress. Here, we report the crystal structure of murine GSTA4-4, which is the first structure of a prototypical member of this subgroup. The structure was solved by molecular replacement and refined to 2.9 A resolution. It resembles the structure of other members of the GST superfamily, but reveals a distinct substrate binding site.

Animals↗

PubMed1998

Accelerated X-ray structure elucidation of a 36 kDa muramidase/transglycosylase using wARP.

The X-ray structure of the 36 kDa soluble lytic transglycosylase from Escherichia coli has been determined starting with the multiple isomorphous replacement method with inclusion of anomalous scattering at 2.7 A resolution. Subsequently, before any model building was carried out, phases were extended to 1.7 A resolution with the weighted automated refinement procedure wARP, which gave a dramatic improvement in the phases. The electron-density maps from wARP were of outstanding quality for both the main chain and the side chains of the protein, which allowed the time spent on the tracing, interpretation and building of the X-ray structure to be substantially shortened. The structure of the soluble lytic transglycosylase was refined at 1.7 A resolution with X-PLOR to a final crystallographic R factor of 18.9%. Analysis of the wARP procedure revealed that the use of the maximum-likelihood refinement in wARP gave much better phases than least-squares refinement, provided that the ratio of reflections to protein atom parameters was approximately 1.8 or higher. Furthermore, setting aside 5% of the data for an Rfree test set had a negative effect on the phase improvement. The mean WwARP, a weight determined at the end of the wARP procedure and based on the variance of structure factors from six individually refined wARP models, proved to be a better indicator than the Rfree factor to judge different phase improvement protocols. The elongated Slt35 structure has three domains named the alpha, beta and core domains. The alpha domain contains mainly alpha-helices, while the beta domain consists of a five-stranded antiparallel beta-sheet flanked by a short alpha-helix. Sandwiched between the alpha and beta domains is the core domain, which bears some resemblance to the fold of the catalytic domain of the previously elucidated 70 kDa soluble lytic transglycosylase from E. coli. The putative active site is at the bottom of a large deep groove in the core domain.

Automation↗

PubMed1997

Three-dimensional structure of L-2-haloacid dehalogenase from Xanthobacter autotrophicus GJ10 complexed with the substrate-analogue formate.

The L-2-haloacid dehalogenase from the 1,2-dichloroethane degrading bacterium Xanthobacter autotrophicus GJ10 catalyzes the hydrolytic dehalogenation of small L-2-haloalkanoic acids to yield the corresponding D-2-hydroxyalkanoic acids. Its crystal structure was solved by the method of multiple isomorphous replacement with incorporation of anomalous scattering information and solvent flattening, and was refined at 1.95-A resolution to an R factor of 21.3%. The three-dimensional structure is similar to that of the homologous L-2-haloacid dehalogenase from Pseudomonas sp. YL (1), but the X. autotrophicus enzyme has an extra dimerization domain, an active site cavity that is completely shielded from the solvent, and a different orientation of several catalytically important amino acid residues. Moreover, under the conditions used, a formate ion is bound in the active site. The position of this substrate-analogue provides valuable information on the reaction mechanism and explains the limited substrate specificity of the Xanthobacter L-2-haloacid dehalogenase.

Binding Sites↗

PubMed1997

X-ray structure of antistasin at 1.9 A resolution and its modelled complex with blood coagulation factor Xa.

The three-dimensional structure of antistasin, a potent inhibitor of blood coagulation factor Xa, from the Mexican leech Haementeria officinalis was determined at 1.9 A resolution by X-ray crystallography. The structure reveals a novel protein fold composed of two homologous domains, each resembling the structure of hirustasin, a related 55-residue protease inhibitor. However, hirustasin has a different overall shape than the individual antistasin domains, it contains four rather than two beta-strands, and does not inhibit factor Xa. The two antistasin domains can be subdivided into two similarly sized subdomains with different relative orientations. Consequently, the domain shapes are different, the N-terminal domain being wedge-shaped and the C-terminal domain flat. Docking studies suggest that differences in domain shape enable the N-terminal, but not C-terminal, domain of antistasin to bind and inhibit factor Xa, even though both have a very similar reactive site. Furthermore, a putative exosite binding region could be defined in the N-terminal domain of antistasin, comprising residues 15-17, which is likely to interact with a cluster of positively charged residues on the factor Xa surface (Arg222/Lys223/Lys224). This exosite binding region explains the specificity and inhibitory potency of antistasin towards factor Xa. In the C-terminal domain of antistasin, these exosite interactions are prevented due to the different overall shape of this domain.

Amino Acid Sequence↗

PubMed1997

The structure of an energy-coupling protein from bacteria, IIBcellobiose, reveals similarity to eukaryotic protein tyrosine phosphatases.

BACKGROUND: . The bacterial phosphoenolpyruvate-dependent phosphotransferase system (PTS) mediates the energy-driven uptake of carbohydrates and their concomitant phosphorylation. In addition, the PTS is intimately involved in the regulation of a variety of metabolic and transcriptional processes in the bacterium. The multiprotein PTS consists of a membrane channel and at least four cytoplasmic proteins or protein domains that sequentially transfer a phosphoryl group from phosphoenolpyruvate to the transported carbohydrate. Determination of the three-dimensional structure of the IIB enzymes within the multiprotein complex would provide insights into the mechanisms by which they promote efficient transport by the membrane channel IIC protein and phosphorylate the transported carbohydrate on the inside of the cell. RESULTS: . The crystal structure of the IIB enzyme specific for cellobiose, IIBcellobiose (molecular weight 11.4 kDa), has been determined to a resolution of 1.8 and refined to an R factor of 18.7% (Rfree of 24. 1%). The enzyme consists of a single four-stranded parallel beta sheet flanked by helices on both sides. The phosphorylation site (Cys 10) is located at the C-terminal end of the first beta strand. No positively charged residues, which could assist in phosphoryl-transfer, can be found in or near the active site. The fold of IIBcellobiose is remarkably similar to that of the mammalian low molecular weight protein tyrosine phosphatases. CONCLUSIONS: . A comparison between IIBcellobiose and the structurally similar low molecular weight protein tyrosine phosphatases provides insight into the mechanism of the phosphoryltransfer reactions in which IIBcellobiose is involved. The differences in tertiary structure and active-site composition between IIBcellobiose and the glucose-specific IIBglucose give a structural explanation why the carbo-hydrate-specific components of different families cannot complement each other.

Animals↗

PubMed1996

The raw starch binding domain of cyclodextrin glycosyltransferase from Bacillus circulans strain 251.

The E-domain of cyclodextrin glycosyltransferase (CGTase) (EC 2.4.1.19) from Bacillus circulans strain 251 is a putative raw starch binding domain. Analysis of the maltose-dependent CGTase crystal structure revealed that each enzyme molecule contained three maltose molecules, situated at contact points between protein molecules. Two of these maltoses were bound to specific sites in the E-domain, the third maltose was bound at the C-domain. To delineate the roles in raw starch binding and cyclization reaction kinetics of the two maltose binding sites in the E-domain, we replaced Trp-616 and Trp-662 of maltose binding site 1 and Tyr-633 of maltose binding site 2 by alanines using site-directed mutagenesis. Purified mutant CGTases were characterized with respect to raw starch binding and cyclization reaction kinetics on both soluble and raw starch. The results show that maltose binding site 1 is most important for raw starch binding, whereas maltose binding site 2 is involved in guiding linear starch chains into the active site. beta-Cyclodextrin causes product inhibition by interfering with catalysis in the active site and the function of maltose binding site 2 in the E-domain. CGTase mutants in the E-domain maltose binding site 1 could no longer be crystallized as maltose-dependent monomers. Instead, the W616A mutant CGTase protein was successfully crystallized as a carbohydrate-independent dimer; its structure has been refined to 2.2 A resolution. The three-dimensional structure shows that, within the error limits, neither the absence of carbohydrates nor the W616A mutation caused significant further conformational changes. The modified starch binding and cyclization kinetic properties observed with the mutant CGTase proteins thus can be directly related to the amino acid replacements.

Amino Acid Sequence↗

PubMed1996

Kinetic characterization and X-ray structure of a mutant of haloalkane dehalogenase with higher catalytic activity and modified substrate range.

Conversion of halogenated aliphatics by haloalkane dehalogenase proceeds via the formation of a covalent alkyl-enzyme intermediate which is subsequently hydrolyzed by water. In the wild type enzyme, the slowest step for both 1,2-dichloroethane and 1,2-dibromoethane conversion is a unimolecular enzyme isomerization preceding rapid halide dissociation. Phenylalanine 172 is located in a helix-loop-helix structure that covers the active site cavity of the enzyme, interacts with the C1 beta of 1,2-dichloroethane during catalysis, and could be involved in stabilization of this helix-loop-helix region of the cap domain of the enzyme. To obtain more information about the role of this residue in dehalogenase function, we performed a mutational analysis of position 172 and studied the kinetics and X-ray structure of the Phe172Trp enzyme. The Phe172Trp mutant had a 10-fold higher Kcat/Km for 1-chlorohexane and a 2-fold higher Kcat for 1,2-dibromoethane than the wild-type enzyme. The X-ray structure of the Phe172Trp enzyme showed a local conformational change in the helix-loop-helix region that covers the active site. This could explain the elevated activity for 1-chlorohexane of the Phe172Trp enzyme, since it allows this large substrate to bind more easily in the active site cavity. Pre-steady-state kinetic analysis showed that the increase in Kcat found for 1,2-dibromoethane conversion could be attributed to an increase in the rate of an enzyme isomerization step that preceeds halide release. The observed conformational difference between the helix-loop-helix structures of the wild-type enzyme and the faster mutant suggests that the isomerization required for halide release could be a conformational change that takes place in this region of the cap domain of the dehalogenase. It is proposed that Phe172 is involved in stabilization of the helix-loop-helix structure that covers the active site of the enzyme and creates a rigid hydrophobic cavity for small apolar halogenated alkanes.

Amino Acids↗

PubMed1996

Nitrate binding to Limulus polyphemus subunit type II hemocyanin and its functional implications.

The horseshoe crab, Limulus polyphemus, employs hemocyanin as an oxygen carrier in its hemolymph. This hemocyanin displays cooperative oxygen binding and heterotropic allosteric regulation by protons, chloride ions and divalent cations. Here, we report the crystal structure of Limulus polyphemus subunit type II hemocyanin with a nitrate ion bound in the interface of its first and second domains. Interestingly, the nitrate-binding site coincides with the binding site for the allosteric effector chloride. Oxygen-binding data indeed indicate that nitrate, like chloride, reduces the oxygen affinity of this hemocyanin. The observed binding of two distinct anions to a single site suggests that several other anions may also bind at this site. This opens the intriguing possibility that bicarbonate, which is structurally similar to nitrate and closely linked to respiration, can act as an allosteric effector that lowers the oxygen affinity. Such an effect could be another factor in the repertoire of allosteric regulators of this hemocyanin; however, the physiological implications will be a challenge to decipher, since there exists a complex interplay of effects between bicarbonate, chloride, pH and divalent cations.

Animals↗

PubMed1996

Crystallization and preliminary crystallographic analysis of endo-1,4-beta-xyalanase I from Aspergillus niger.

A family G xylanase from Aspergillus niger has been crystallized using the vapor-diffusion method. Several crystal forms could be obtained using various sodium salts as precipitants. Three of the crystal forms belong to space groups P21, P2(1)2(1)2(1) and P4(3) and have cell parameters of approximately a = b = 85.1, c = 113.6 A and alpha = beta = gamma = 90 degrees. These crystal forms can be converted into one another by flash freezing or macroseeding. A fourth crystal form is cubic (space group P2(1)3) with unit-cell axes of a = b = c = 112.3 A. Data sets for three of the four crystal forms have been collected, extending to a maximum resolution of 2.4 A. The structures of the monoclinic and orthorhombic crystals have been solved by molecular replacement by combining the crystallographic information of the different crystal forms. Refinement of the orthorhombic crystal form is now in progress.

Journal Article↗

PubMed1996

Structure of cyclodextrin glycosyltransferase complexed with a maltononaose inhibitor at 2.6 angstrom resolution. Implications for product specificity.

Crystals of the Y195F mutant of cyclodextrin glycosyltransferase from Bacillus circulans strain 251 were subjected to a double soaking procedure, in which they were first soaked in a solution containing the inhibitor acarbose and subsequently in a solution containing maltohexaose. The refined structure of the resulting protein-carbohydrate complex has final crystallographic and free R-factors for data in the 8-2.6 angstrom resolution range of 15.0% and 21.5%, respectively, and reveals that a new inhibitor, composed of nine saccharide residues, is bound in the active site. The first four residues correspond to acarbose and occupy the same subsites near the catalytic residues as observed in the previously reported acarbose-enzyme complex [Strokopytov et al. (1995) Biochemistry 34, 2234-2240]. An oliogosaccharide consisting of five glucose residues has been coupled to the nonreducing end of acarbose. At the fifth residue the polysaccharide chain makes a sharp turn, allowing it to interact with residues Tyr89, Phe195, and Asn193 and a flexible loop formed by residues 145-148. On the basis of the refined model of the complex an explanation is given for the product specificity of CGTases.

Amino Acid Sequence↗

PubMed1996

Crystal structure at 2.3 A resolution and revised nucleotide sequence of the thermostable cyclodextrin glycosyltransferase from Thermonanaerobacterium thermosulfurigenes EM1.

The crystal structure of the cyclodextrin glycosyltransferase (CGTase) from the thermophilic microorganism Thermoanaerobacterium thermosulfurigenes EM1 has been elucidated at 2.3 A resolution. The final model consists of all 683 amino acid residues, two calcium ions and 343 water molecules, and has a crystallographic R-factor of 17.9% (Rfree 24.9%) with excellent stereochemistry. The overall fold of the enzyme is highly similar to that reported for mesophilic CGTases and differences are observed only at surface loop regions. Closer inspection of these loop regions and comparison with other CGTase structures reveals that especially loops 88-95, 335-339 and 534-539 possibly contribute with novel hydrogen bonds and apolar contacts to the stabilization of the enzyme. Other structural features that might confer thermostability to the T. thermosulfurigenes EM1 CGTase are the introduction of five new salt-bridges and three Gly to Ala/Pro substitutions. The abundance of Ser, Thr and Tyr residues near the active site and oligosaccharide binding sites might explain the increased thermostability of CGTase in the presence of starch, by allowing amylose chains to bind non-specifically to the protein. Additional stabilization of the A/E domain interface through apolar contacts involves residues Phe273 and Tyr187. No additional or improved calcium binding is observed in the structure, suggesting that the observed stabilization in the presence of calcium ions is caused by the reduced exchange of calcium from the protein to the solvent, rendering it less susceptible to unfolding. The 50% decrease in cyclization activity of the T. thermosulfurigenes EM1 CGTase compared with that of B. circulans strain 251 appears to be caused by the changes in the conformation and amino acid composition of the 88-95 loop. In the T. thermosulfurigenes EM1 CGTase there is no residue homologous to Tyr89, which was observed to take part in stacking interactions with bound substrate in the case of the B. circulans strain 251 CGTase. The lack of this interaction in the enzyme-substrate complex is expected to destabilize bound substrates prior to cyclization. Apparently, some catalytic functionality of CGTase has been sacrificed for the sake of structural stability by modifying loop regions near the active site.

Amino Acid Sequence↗

PubMed1995

Crystallographic studies of the interaction of cyclodextrin glycosyltransferase from Bacillus circulans strain 251 with natural substrates and products.

Asp-229, Glu-257, and Asp-328 constitute the catalytic residues in cyclodextrin glycosyl transferase from Bacillus circulans strain 251. Via site-directed mutagenesis constructed D229N, E257Q, and D328N mutant proteins showed a 4,000-60,000-fold reduction of cyclization activity. A D229N/E257Q double mutant showed a 700,000-fold reduction and was crystallized for use in soaking experiments with alpha-cyclodextrin. Crystal structures were determined of wild type CGTase soaked at elevated pH with alpha-cyclodextrin (resolution, 2.1 A) and maltoheptaose (2.4 A). In addition, structures at cryogenic temperature were solved of the unliganded enzyme (2.2 A) and of the D229N/E257Q mutant after soaking with alpha-cyclodextrin (2.6 A). In the crystals soaked in alpha-cyclodextrin and maltoheptaose, a maltotetraose molecule is observed to bind in the active site. Residue 229 is at hydrogen bonding distance from the C-6 hydroxyl group of the sugar, which after cleavage will contain the new reducing end. In the D229N/E257Q double mutant structure, two alpha-cyclodextrins are observed to replace two maltoses at the E-domain, thus providing structural information on product inhibition via binding to the enzyme's raw starch binding domain.

Bacillus↗

PubMed1995

Stereochemistry of chitin hydrolysis by a plant chitinase/lysozyme and X-ray structure of a complex with allosamidin: evidence for substrate assisted catalysis.

The plant enzyme hevamine has both chitinase and lysozyme activity. HPLC analysis of the products of the hydrolysis of chitopentaose shows that hevamine acts with retention of the configuration, despite the absence of a nucleophilic or stabilizing carboxylate. To analyze the stabilization of a putative oxocarbonium ion intermediate, the X-ray structure of hevamine complexed with the inhibitor allosamidin was determined at 1.85 A resolution. This structure supports the role of Glu127 as a proton donor. The allosamizoline group binds in the center of the active site, mimicking a reaction intermediate in which a positive charge at C1 is stabilized intramolecularly by the carbonyl oxygen of the N-acetyl group at C2.

Acetylglucosamine↗

PubMed1995

Structure of the 70-kDa soluble lytic transglycosylase complexed with bulgecin A. Implications for the enzymatic mechanism.

Bulgecins are O-sulfonated glycopeptides that are able to enhance the antibacterial activity of beta-lactam antibiotics. The 70-kDa soluble lytic transglycosylase (SLT70) from Escherichia coli forms a specific target of these compounds. Using X-ray crystallography, the three-dimensional structure of a complex of SLT70 with bulgecin A has been determined to 2.8-A resolution and refined to an R factor of 19.5%. The model contains all 618 amino acids of SLT70 and a single molecule of bound bulgecin, located in the active site of the enzyme. The glycopeptide inhibitor is bound in an extended conformation occupying sites analogous to the B, C, and D subsites of lysozyme. Upon binding of bulgecin, the three-stranded antiparallel beta-sheet in the C domain shows a pronounced shift toward the inhibitor. In subsite D, the proposed catalytic residue Glu478 forms a hydrogen bond to the hydroxymethyl oxygen of the proline part of bulgecin and interacts electrostatically with the proline NH2+ group. These interactions, in addition to the interactions observed for the 2-acetamido group of the N-acetylglucosamine residue bound in subsite C, may explain the strong inhibition of SLT70 activity by bulgecin, suggesting that bulgecin acts as an analogue of an oxocarbonium ion intermediate in the reaction catalyzed by SLT70. The structure of the SLT70--bulgecin A complex may be of assistance in the rational design of novel antibiotics.

Bacterial Proteins↗

PubMed1995

Crystallization and preliminary X-ray analysis of outer membrane phospholipase A from Escherichia coli.

The outer membrane phospholipase A (OMPLA) of Escherichia coli is one of the few integral outer membrane proteins displaying enzymatic activity. It is encoded as a mature protein of 269 amino acids preceded by a signal sequence of 20 amino acids. There is no sequence homology with water-soluble lipases and phospholipases. Crystals of the mature enzyme were obtained at 22 degrees C from 24-28% (v/v) 2-methyl-2,4-pentanediol in Bis-Tris buffer, pH 5.9-6.0, with 1 mM calcium chloride and 1.5% (w/v) beta-octylglucoside. They have the symmetry of the trigonal spacegroup P3(1)21 (or P3(2)21) with cell dimensions of a = b = 79.6 A and c = 102.8 A (alpha = beta = 90 degrees, gamma = 120 degrees). Native crystals diffract to a resolution of 2.6 A.

Amino Acid Sequence↗

PubMed1995

X-ray structure of cyclodextrin glycosyltransferase complexed with acarbose. Implications for the catalytic mechanism of glycosidases.

Crystals of cyclodextrin glycosyltransferase (CGTase) from Bacillus circulans strain 251 were soaked in buffer solutions containing the pseudotetrasaccharide acarbose, a strong amylase- and CGTase inhibitor. The X-ray structure of the complex was elucidated at 2.5-A resolution with a final crystallographic R value of 15.8% for all data between 8.0 and 2.5 A. Acarbose is bound near the catalytic residues Asp229, Glu257, and Asp328. The carboxylic group of Glu257 is at hydrogen bonding distance from the glycosidic oxygen in the scissile bond between the B and C sugars (residue A is at the nonreducing end of the inhibitor). Asp328 makes hydrogen bonds with the 4-amino-4,6-dideoxyglucose (residue B), and Asp229 is in a close van der Waals contact with the C1 atom of this sugar. From this we conclude that in CGTase Glu257 acts as the proton donor and Asp229 serves as the general base or nucleophile, while Asp328 is involved in substrate binding and may be important for elevating the pKa of Glu257. On the basis of these results it appears that the absence of the C6-hydroxyl group in the B sugar is responsible for the inhibitory properties of acarbose on CGTase. This suggests that the C6-hydroxyl group of this sugar plays an essential role in the catalytic mechanism of CGTase.(ABSTRACT TRUNCATED AT 250 WORDS)

Acarbose↗