Substrate-based protein engineering of a flavoprotein oxidase for improved alcohol over-oxidation

The oxidation of alcohols to the corresponding carbonyl compounds represents a convenient strategy for the selective introduction of carbon-acceptor units into carbohydrate-based starting materials from renewable resources. A simple system to accomplish this transformation is by using flavin-containing alcohol oxidases. However, with prim-alcohols, the oxidation does not necessarily stop at the aldehyde stage, but may furnish the carboxylic acid via \u27over\u27-oxidation of the aldehyde hydrate.[1] In order to develop an alcohol oxidase for the efficient transformation of alcohols into carboxylic acids, we chose the recently discovered (5-hydroxymethyl)furfural oxidase (HMFO), which converts not only the eponymous (5-hydroxymethyl)furfural, but also a range of aromatic and allylic alcohols (Figure 1).[2]In order to improve the performance of HMFO for over-oxidation, we anticipated an improved stabilisation of the aldehyde hydrate in the active site to be a crucial factor. After inspection of the HMFO crystal structure, two positions were identified, where hydrogen bond donating and accepting amino acids were introduced, in order to stabilize the gem-diol moiety.[3] Indeed, one of the new HMFO variants exhibited a significantly increased activity for the formation of carboxylic acids from benzylic alcohols. Please click Additional Files below to see the full abstract

Begrenzen Chinas Wasserressourcen seine wirtschaftliche Entwicklung?

Dieses Papier untersucht Probleme der Wasserverfügbarkeit in China. Es wird gezeigt, dass - geographisch bedingt - erhebliche regionale Unterschiede in der Verfügbarkeit von Wasser in China existieren. Eine empirische Analyse der regionalen Strukturen der Wasserverfügbarkeit und des Wasserverbrauches für den Konsum sowie die landwirtschaftliche und industrielle Produktion zeigt, dass insbesondere erhebliche Nutzungskonflikte zwischen Landwirtschaft und Industrie existieren. Ein Szenario zur möglichen künftigen Entwicklung zeigt darüber hinaus, dass sich diese Nutzungskonflikte weiter verschärfen werden. Die damit verbundenen Probleme lassen sich nur durch eine Verbesserung der Effizienz der Wassernutzung verbunden mit einem umfangreichen Transfer von Wasser aus dem Süden in den Norden des Landes lösen. Ohne diese Maßnahmen können die natürlichen Bedingungen zu einer bindenden Restriktion für die künftige wirtschaftliche Entwicklung Chinas werden.Wasserressourcen, wirtschaftliche Entwicklung, Umweltprobleme

Asymmetric bioreduction of activated alkenes to industrially relevant optically active compounds

AbstractEne-reductases from the ‘Old Yellow Enzyme’ family of flavoproteins catalyze the asymmetric reduction of various α,β-unsaturated compounds at the expense of a nicotinamide cofactor. They have been applied to the synthesis of valuable enantiopure products, including chiral building blocks with broad industrial applications, terpenoids, amino acid derivatives and fragrances. The combination of these highly stereoselective biocatalysts with a cofactor recycling system has allowed the development of cost-effective methods for the generation of optically active molecules, which is strengthened by the availability of stereo-complementary enzyme homologues

Asymmetric Synthesis of b-Substituted a-Methylenebutyro- lactones via TRIP-Catalyzed Allylation: Mechanistic Studies and Application to the Synthesis of (S)-(À)-Hydroxymatairesinol

Abstract: Asymmetric allylation of (hetero)aromatic aldehydes by a zinc(II)-allylbutyrolactone species catalyzed by a chiral BINOL-type phosphoric acid gave b-substituted a-methylenebutyrolactones in 68 to > 99% ee and 52-91% isolated yield. DFT studies on the intermediate Zn 2+ -complex -crucial for chiral induction -suggest a six-membered ring intermediate, which allows the phosphoric acid moiety to activate the aldehyde. The methodology was applied to the synthesis of the antitumour natural product (S)-(À)-hydroxymatairesinol

Vortex structures in pure SU(3) lattice gauge theory

The structures of confining vortices which underlie pure SU(3) Yang-Mills theory are studied by means of lattice gauge theory. Vortices and Z_3 monopoles are defined as dynamical degrees of freedom of the Z_3 gauge theory which emerges by center gauge fixing and by subsequent center projection. It is observed for the first time for the case of SU(3) that these degrees of freedom are sensible in the continuum limit: the planar vortex density and the monopole density properly scales with the lattice spacing. By contrast to earlier findings concerning the gauge group SU(2), the effective vortex theory only reproduces 62% of the full string tension. On the other hand, however, the removal of the vortices from the lattice configurations yields ensembles with vanishing string tension. SU(3) vortex matter which originates from Laplacian center gauge fixing is also discussed. Although these vortices recover the full string tension, they lack a direct interpretation as physical degrees of freedom in the continuum limit.Comment: 25 pages, 13 ps figures, improved presentation, results unchange

Stereoselective synthesis of γ-hydroxynorvaline through combination of organo- and biocatalysis

An efficient route for the synthesis of all four diastereomers of PMP-protected α-amino-γ-butyrolacton to access γ-hydroxynorvaline was established. The asymmetric key steps comprise an organocatalytic Mannich reaction and an enzymatic ketone reduction. Three reaction steps could be integrated in a one-pot process, using 2-PrOH both as solvent and as reducing agent. The sequential construction of stereogenic centres gave access to each of the four stereoisomers in high yield and with excellent stereocontrol

Structural and Mechanistic Analysis of the Choline Sulfatase from Sinorhizobium melliloti: A Class I Sulfatase Specific for an Alkyl Sulfate Ester.

Hydrolysis of organic sulfate esters proceeds by two distinct mechanisms, water attacking at either sulfur (S-O bond cleavage) or carbon (C-O bond cleavage). In primary and secondary alkyl sulfates, attack at carbon is favored, whereas in aromatic sulfates and sulfated sugars, attack at sulfur is preferred. This mechanistic distinction is mirrored in the classification of enzymes that catalyze sulfate ester hydrolysis: arylsulfatases (ASs) catalyze S-O cleavage in sulfate sugars and arylsulfates, and alkyl sulfatases break the C-O bond of alkyl sulfates. Sinorhizobium meliloti choline sulfatase (SmCS) efficiently catalyzes the hydrolysis of alkyl sulfate choline-O-sulfate (kcat/KM=4.8×103s-1M-1) as well as arylsulfate 4-nitrophenyl sulfate (kcat/KM=12s-1M-1). Its 2.8-Å resolution X-ray structure shows a buried, largely hydrophobic active site in which a conserved glutamate (Glu386) plays a role in recognition of the quaternary ammonium group of the choline substrate. SmCS structurally resembles members of the alkaline phosphatase superfamily, being most closely related to dimeric ASs and tetrameric phosphonate monoester hydrolases. Although >70% of the amino acids between protomers align structurally (RMSDs 1.79-1.99Å), the oligomeric structures show distinctly different packing and protomer-protomer interfaces. The latter also play an important role in active site formation. Mutagenesis of the conserved active site residues typical for ASs, H218O-labeling studies and the observation of catalytically promiscuous behavior toward phosphoesters confirm the close relation to alkaline phosphatase superfamily members and suggest that SmCS is an AS that catalyzes S-O cleavage in alkyl sulfate esters with extreme catalytic proficiency

Vortex critical behavior at the de-confinement phase transition

The de-confinement phase transition in SU(2) Yang-Mills theory is revisited in the vortex picture. Defining the world sheets of the confining vortices by maximal center projection, the percolation properties of the vortex lines in the hypercube consisting of the time axis and two spatial axis are studied. Using the percolation cumulant, the temperature for the percolation transition is seen to be in good agreement with the critical temperature of the thermal transition. The finite size scaling function for the cumulant is obtained. The critical index of the finite size scaling function is consistent with the index of the 3D Ising model.Comment: 4 pages, 4 PS figures, using revtex4, paragraph and refs added, typo correcte

Vortex dominance of the 0+ and 2+ glueball mass in SU(2) lattice gauge theory

The c-vortex ensembles are constructed by means of the recently proposed cooling method which gradually removes the SU(2)/Z_2 coset fields from the SU(2) lattice configurations and which thus reveals the Z_2 vortex vacuum texture. Using Teper's blocking method, the screening masses of the 0+ and the 2+ glueball is calculated from these vortex ensembles and compared with the masses obtained from full configurations. The masses of either case agree within the achieved numerical accuracy of 10%. As a byproduct, we find that the overlaps of the Teper operators with the glueball wavefunctions are significantly larger in the case of the c-vortex ensembles.Comment: 9 pages, 4 PS figures, LaTeX using eps