Anomer Selective Formation of l-Menthyl α-D-Glucopyranoside by α-Glucosidase-catalyzed Reaction

l-Menthol was glucosylated by the α-glucosidase (EC 3.2.1.20) of Saccharomyces cerevisiae using maltose as glucosyl donor. When 50 mg of l-menthol and 1M maltose in 10 mM citrate–phosphate buffer (pH 7.0) were incubated for 24 h at 30°C, a menthylglucoside was selectively obtained as a product. The molar conversion yield based on supplied menthol was 4.5%. The product was identified as l-menthyl α-D-glucopyranoside (α-MenG) by ¹³C-NMR analysis.     

Acceleration of α-Synuclein Aggregation by Exosomes

Exosomes are small vesicles released from cells into extracellular space. We have isolated exosomes from neuroblastoma cells and investigated their influence on the aggregation of α-synuclein, a protein associated with Parkinson disease pathology. Using cryo-transmission electron microscopy of exosomes, we found spherical unilamellar vesicles with a significant protein content, and Western blot analysis revealed that they contain, as expected, the proteins Flotillin-1 and Alix. Using thioflavin T fluorescence to monitor aggregation kinetics, we found that exosomes catalyze the process in a similar manner as a low concentration of preformed α-synuclein fibrils. The exosomes reduce the lag time indicating that they provide catalytic environments for nucleation. The catalytic effects of exosomes derived from naive cells and cells that overexpress α-synuclein do not differ. Vesicles prepared from extracted exosome lipids accelerate aggregation, suggesting that the lipids in exosomes are sufficient for the catalytic effect to arise. Using mass spectrometry, we found several phospholipid classes in the exosomes, including phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine, phosphatidylinositol, and the gangliosides GM2 and GM3. Within each class, several species with different acyl chains were identified. We then prepared vesicles from corresponding pure lipids or defined mixtures, most of which were found to retard α-synuclein aggregation. As a striking exception, vesicles containing ganglioside lipids GM1 or GM3 accelerate the process. Understanding how α-synuclein interacts with biological membranes to promote neurological disease might lead to the identification of novel therapeutic targets.     

The metabolism of α-tocopherol by plants

An enzyme system which metabolizes α-tocopherol has been identified in homogenates of etiolated pea shoots. Enzyme activity is considerably increased by the presence of 20% ethanol in the incubation mixture. The enzyme has an absolute requirement for phospholipid. The reaction utilizes molecular oxygen and it is proposed that the enzyme be called α-tocopherol oxidase.     

Activation of α-secretase by curcumin-aminoacid conjugates

The extracellular senile plaques observed in Alzheimer's disease (AD) patients are mainly composed of amyloid peptides produced from the β-amyloid precursor protein (βAPP) by β- and γ-secretases. A third non-amyloidogenic α-secretase activity performed by the disintegrins ADAM10 and ADAM17 occurs in the middle of the amyloid-β peptide Aβ and liberates the large sAPPα neuroprotective fragment. Since the activation of α-secretase recently emerged as a promising therapeutic approach to treat AD, the identification of natural compounds able to trigger this cleavage is highly required. Here we describe new curcumin-based modified compounds as α-secretase activators. We established that the aminoacid conjugates curcumin-isoleucine, curcumin-phenylalanine and curcumin-valine promote the constitutive α-secretase activity and increase ADAM10 immunoreactivity. Strickingly, experiments carried out under conditions mimicking the PKC/muscarinic receptor-regulated pathway display different patterns of activation by these compounds. Altogether, our data identified new lead natural compounds for the future development of powerful and stable α-secretase activators and established that some of these molecules are able to discriminate between the constitutive and regulated α-secretase pathways.     

Syntheses of α-tocopheryl glycosides by glucosidases

Enzymatic syntheses of water-soluble alpha-tocopheryl glycosides were carried out in di-isopropyl ether using amyloglucosidase from Rhizopus mold or beta-glucosidase isolated from sweet almond. Optimum conditions for the amyloglucosidase were: alpha-tocopherol 0.5 mmol, D-glucose 0.5 mmol, 400 activity unit (AU) amyloglucosidase, 0.2 mM pH 7 phosphate buffer and 72 h; and for the beta-glucosidase: alpha-tocopherol 0.5 mmol, D: -glucose 0.5 mmol, 110 AU beta-glucosidase, 0.1 mM pH 6 phosphate buffer and 72 h. Out of 11 carbohydrates employed, amyloglucosidase reacted only with D-glucose to give 50% of 6-O-(alpha-D-glucopyranosyl)alpha-tocopherol. However, the beta-glucosidase gave 6-O-(beta-D-glucopyranosyl)alpha-tocopherol, 6-O-(alpha-D-galactopyranosyl)alpha-tocopherol, 6-O-(beta-D-galactopyranosyl)alpha-tocopherol, 6-O-(alpha-D-mannopyranosyl)alpha-tocopherol and 6-O-(beta-D-mannopyranosyl)alpha-tocopherol in yields ranging from 10-25%. Water solubility of 6-O-(alpha-D-glucopyranosyl)alpha-tocopherol was 26 g/l at 25 degrees C. alpha-Tocopheryl glycosides showed antioxidant activities with IC(50) values from 0.5 to 1 mM and angiotensin-converting enzyme (ACE) inhibitory activity with IC(50) values from 1.3 to 2.6 mM.     

Conformational Changes of αs-Casein by Heating

Conformational changes of α_s-casein by heating were investigated by measuring ultraviolet difference spectra. The ultraviolet difference spectra at elevated temperature against 5.5°C were measured in various ionic strengths and pHs. Thermal effects of the difference spectra were cancelled by comparing with the spectra of model compounds such as lysozyme and ribonuclease, and the blue shift of α_s-casein spectra was observed at above 30°C in these all experimental conditions. This shift was considered to mean unfolding of the α_s-casein molecule. The aggregation of α_s-casein was observed above ionic strength of 0.4 by heating. These heat-induced changes were reversible until the aggregation was observed.     

Denitration of carbohydrate α-nitroepoxides by nucleophiles

Several nucleophiles were separately treated with methyl and phenyl 2,3-anhydro-4,6-O-benzylidene-3-deoxy-3-nitro-β-d-allopyranoside, to give 2-substituted aldos-3-ulose derivatives. In the latter case, the subsequent β-elimination of the aglyconic phenyl group always occurred to afford the corresponding glycal. Reaction mechanisms thereof are also discussed.     

Synthesis of α-galacto-oligosaccharides by a cloned α-galactosidase from Bifidobacterium adolescentis

A genomic library of Bifidobacterium adolescentis was constructed in Escherichia coli and a gene encoding an -galactosidase was isolated. The identified open reading frame showed high similarity and identity with bacterial -galactosidases, which belong to Family 36 of the glycosyl hydrolases. For the purification of the enzyme from the medium a single chromatography step was sufficient. The yield of the recombinant enzyme was 100 times higher than from B. adolescentis itself. In addition to hydrolytic activity the -galactosidase showed transglycosylation activity and can be used for the production of -galacto-oligosaccharides.     

Condensation reactions catalyzed by α-N-acetylgalactosaminidase from Aspergillus niger yielding α-N-acetylgalactosaminides

Abstract

Extracellular α-N-acetylgalactosaminidase from Aspergillus niger catalyzed glycosylation yielding a series of 2-acetamido-2-deoxy-α-D-galactobiosides using 2-acetamido-2-deoxy-D-galactopyranose as a glycosyl donor. The isomers α-D-GalpNAc-(1→6)-D-GalpNAc, α-D-GalpNAc-(1→3)-D-GalpNAc and α-D-GalpNAc-(1→6)-D-GalfNAc were isolated and spectrally characterized. The purified enzyme was further used for the glycosylation of free amino acids (serine and threonine) and their N-(tert-butoxycarbonyl)-protected analogs to synthesize the Tn antigen (GalpNAc-α-O-Ser/Thr) and its N-(tert-butoxycarbonyl)-protected derivatives.     

Differential glycosylation of α-dystroglycan and proteins other than α-dystroglycan by like-glycosyltransferase

Genetic defects in like-glycosyltransferase (LARGE) cause congenital muscular dystrophy with central nervous system manifestations. The underlying molecular pathomechanism is the hypoglycosylation of α-dystroglycan (α-DG), which is evidenced by diminished immunoreactivity to IIH6C4 and VIA4-1, antibodies that recognize carbohydrate epitopes. Previous studies indicate that LARGE participates in the formation of a phosphoryl glycan branch on O-linked mannose or it modifies complex N- and mucin O-glycans. In this study, we overexpressed LARGE in neural stem cells deficient in protein O-mannosyltransferase 2 (POMT2), an enzyme required for O-mannosyl glycosylation. The results showed that overexpressing LARGE did not lead to hyperglycosylation of α-DG in POMT2 knockout (KO) cells but did generate IIH6C4 and VIA4-1 immunoreactivity and laminin-binding activity. Additionally, overexpressing LARGE in cells deficient in both POMT2 and α-DG generated laminin-binding IIH6C4 immunoreactivity. These results indicate that LARGE expression resulted in the glycosylation of proteins other than α-DG in the absence of O-mannosyl glycosylation. The IIH6C4 immunoreactivity generated in double-KO cells was largely removed by treatment either with peptide N-glycosidase F or with cold aqueous hydrofluoric acid, suggesting that LARGE expression caused phosphoryl glycosylation of N-glycans. However, the glycosylation of α-DG by LARGE is dependent on POMT2, indicating that LARGE expression only modifies O-linked mannosyl glycans of α-DG. Thus, LARGE expression mediates the phosphoryl glycosylation of not only O-mannosyl glycans including those on α-DG but also N-glycans on proteins other than α-DG.     

Synthesis of hexyl α-glucoside and α-polyglucosides by a novel Microbacterium isolate

Alkyl-glucosides and alkyl-polyglucosides are the new-generation biodegradable surfactants with good emulsifying and wetting properties. The α-forms of these glucosides occur in antibiotics and also stimulate nasal absorption of many drugs. In this paper, we report the synthesis of hexyl α-glucoside and α-polyglucosides using cell-bound α-glucosidase activity of a novel strain of Microbacterium paraoxydans. A number of cell-bound glycosyl hydrolase activities were detected in the isolate with the maximum hydrolytic activity of 180 IU g^?1 dry wt cells on p-nitrophenyl-α-d-glucopyranoside. In a micro-aqueous system, at a water activity of 0.69, 1.8 g l^?1 of hexyl α-glucoside (corresponding to about 25 % yield) was synthesized by whole cells with maltose and hexanol as substrates. The concentration was enhanced to 11 g l^?1 (~60 % yield) in a biphasic system at a water content of 60 %. ¹H and ¹³C NMR spectra of the purified compound confirmed the synthesized product to be hexyl-α-d-glucopyranoside, while the presence of hexyl di- and tri-glucosides was confirmed by electrospray ionization mass spectrometry. The cell-driven synthesis makes this an extremely attractive alternative for synthesis of such compounds.     

Formation of α-D-glucose-1-phosphate by thermophilic α-1,4-D-glucan phosphorylase

For the production of α-D-glucose-1-phosphate (G-1-P), α-1,4-D-glucan phosphorylase from Thermus caldophilus GK24 was partially purified to a specific activity of 13 U mg⁻¹ and an enzyme recovery of 15%. The amount of G-1-P reached maximum (18%) when soluble starch was used as substrate, and the smallest substrate for G-1-P formation was maltotriose. The structure of purified G-1-P was confirmed by comparison to ¹³C-NMR data for an authentic sample. In addition to G-1-P, glucose-6-phosphate (12%) was simultaneously produced when 10 mM maltoheptaose was used as substrate. Journal of Industrial Microbiology & Biotechnology (2000) 24, 89–93. Received 12 May 1999/ Accepted in revised form 29 August 1999     

High-Yielding Enzymatic α-Glucosylation of Pyridoxine by Marine α-Glucosidase from Aplysia fasciata

We recently succeeded in the identification and purification of an interesting marine exo-α-glucosidase (EC 3.2.1.20) from the anaspidean mollusc Aplysia fasciata. The enzyme was characterized by good transglycosylation activity toward different acceptors using maltose as donor. High-yielding enzymatic α-glycosylation of pyridoxine using this marine enzyme is reported here; the reaction has been optimized, reaching 80% molar yield of products (pyridoxine monoglucosides 24 g/l; pyridoxine isomaltoside 35 g/l). High selectivity toward the 5′ position is observed for both monoglucoside and disaccharide formation. This is the first report describing the enzymatic production of pyridoxine isomaltoside.     

Salt Effects on Plastein Formation by α-Chymotrypsin

The plastein formation by α-chymotrypsin from an ovalbumin hydrolysate was affected in an order of valency of salts when the concentration of each salt was 1 m. Monovalent cations were rather effective at this concentration and enhanced the plastein yield by 10%. In the presence of NaCl, the plastein formation showed two distinct maximal rates at its concentrations of 0.1 m and 0.8 m. The first maximum was considered to be resulted from an increase in enzyme activity, since chymotryptic hydrolysis of both N-acetyl-l-tyrosine ethyl ester and benzyloxycarbonyl-l-phenylalanine p-nitrophenyl ester was activated at an NaCl concentration of 0.1 ~ 0.2 m. The second maximum was ascribed to the salting-out of the product due to the higher concentration of NaCl. A salt-tolerant protease was also used to confirm the above conclusions. It was observed that this enzyme was much effective in producing a plastein at a high NaCl concentration. This may be due to the fact that both the enzyme activation effect and the product salting-out effect participate co-operatively.     

The Inhibition of α-Amylase by Tea Polyphenols

The inhibition of α-amylase from human saliva by polyphenolic components of tea and its specificity was investigated in vitro. Four kinds of green tea catechins, and their isomers and four kinds of their dimeric compounds (theaflavins) produced oxidatively during black tea production were isolated. They were (?)-epicatechin (EC), (?)-epigallocatechin (EGC), (?)-epicatechin gallate (ECg), (?)-epigallocatechin gallate (EGCg), (?)-catechin (C), (?)-gallocatechin (GC), (?)-catechin gallate (Cg), (?)-gallocatechin gallate (GCg), theaflavin (TF1), theaflavin monogallates (TF2A and TF2B), and theaflavin digallate (TF3). Among the samples tested, EC, EGC, and their isomers did not have significant effects on the activity of α-amylase. All the other samples were potent inhibitors and the inhibitory effects were in the order of TF3>TF2A>TF2B>TFl>Cg> GCg > ECg > EGCg. The inhibitory patterns were noncompetitive except for TF3.     

Structural basis for variant-specific neuroligin-binding by α-neurexin

Neurexins (Nrxs) are presynaptic membrane proteins with a single membrane-spanning domain that mediate asymmetric trans-synaptic cell adhesion by binding to their postsynaptic receptor neuroligins. α-Nrx has a large extracellular region comprised of multiple copies of laminin, neurexin, sex-hormone-binding globulin (LNS) domains and epidermal growth factor (EGF) modules, while that of β-Nrx has but a single LNS domain. It has long been known that the larger α-Nrx and the shorter β-Nrx show distinct binding behaviors toward different isoforms/variants of neuroligins, although the underlying mechanism has yet to be elucidated. Here, we describe the crystal structure of a fragment corresponding to the C-terminal one-third of the Nrx1α ectodomain, consisting of LNS5-EGF3-LNS6. The 2.3 Å-resolution structure revealed the presence of a domain configuration that was rigidified by inter-domain contacts, as opposed to the more common flexible “beads-on-a-string” arrangement. Although the neuroligin-binding site on the LNS6 domain was completely exposed, the location of the α-Nrx specific LNS5-EGF3 segment proved incompatible with the loop segment inserted in the B+ neuroligin variant, which explains the variant-specific neuroligin recognition capability observed in α-Nrx. This, combined with a low-resolution molecular envelope obtained by a single particle reconstruction performed on negatively stained full-length Nrx1α sample, allowed us to derive a structural model of the α-Nrx ectodomain. This model will help us understand not only how the large α-Nrx ectodomain is accommodated in the synaptic cleft, but also how the trans-synaptic adhesion mediated by α- and β-Nrxs could differentially affect synaptic structure and function.     

A novel α-glucosidase produced by Bacillus amylolyticus

Bacillus amylolyticus produces -amylase, pullulanase and -glucosidase. By selection of carbon source in the growth medium, -glucosidase was produced preferentially and with exclusion of the other two activities. The -glucosidase was highly specific for maltose and to a lesser extent maltotriose but was inactive towards a range of other substrates including p-nitrophenyl -D-glucoside and isomaltose. Optima for activity were recorded at pH 7.0 and 40° C and the enzyme was insensitive to ethylenediaminetetraacetic acid.