A highly efficient ADH-coupled NADH-recycling system for the asymmetric bioreduction of carbon-carbon double bonds using enoate reductases

The asymmetric bioreduction of activated alkenes catalyzed by flavin-dependent enoate reductases from the OYE-family represents a powerful method for the production of optically active compounds. For its preparative-scale application, efficient and economic NADH-recycling is crucial. A novel enzyme-coupled NADH-recycling system is proposed based on the concurrent oxidation of a sacrificial sec-alcohol catalyzed by an alcohol dehydrogenase (ADH-A). Due to the highly favorable position of the equilibrium of ene-reduction versus alcohol-oxidation, the cosubstrate is only required in slight excess.     

Peptidoglycan remodeling in Mycobacterium tuberculosis: comparison of structures and catalytic activities of RipA and RipB

The success of Mycobacterium tuberculosis in sustaining long-term survival within the host macrophages partly relies on its unique cell envelop that also confers low susceptibility to several antibiotics. Remodeling of the septal peptidoglycan (PG) has been linked to the putative PG hydrolases RipA and RipB. The crystal structures of RipB (Rv1478) and the homologous module of RipA (Rv1477) were determined to 1.60 Å and 1.38 Å resolution, respectively. Both proteins contain a C-terminal core domain resembling the NlpC-type PG hydrolases. However, the structure of RipB exhibits striking differences to the structures of this domain in RipA reported here and previously by others. Major structural differences were found in the N-terminal segments of 70 amino acids and in an adjacent loop, which form part of the substrate binding groove. Both RipA and RipB are able to bind PG. RipA, its C-terminal module and RipB cleave defined PG fragments between d-glutamate and meso-diaminopimelate with pH optima of 5 and 6, respectively. The peptidase module of RipA is also able to degrade Bacillus subtilis PG, which displays peptide stems and cross-links identical with those found in mycobacterial murein. RipB did not show comparable hydrolase activity with this substrate. Removal of the N-terminal segments previously suggested to have a role in auto-inhibition did not change the activity of either RipA or RipB. A comparison of the putative active-site clefts in the two enzymes provides structural insights into the basis of the differences in their substrate specificity.     

Identification and characterization of inhibitors of Haemophilus influenzae acetohydroxyacid synthase

Acetohydroxyacid synthase (AHAS), a potential target for antimicrobial agents, catalyzes the first common step in the biosynthesis of branched-chain amino acids. The gene coding for the AHAS catalytic subunit from Haemophilus influenzae (Hi) was cloned, overexpressed in Escherichia coli, and purified. To identify new inhibitory scaffolds, we used a high-throughput screen to test 221 small diverse chemical compounds against Hi-AHAS. Compounds were selected for their ability to inhibit AHAS in vitro. The screen identified 3 compounds, each representing a structural class, as Hi-AHAS inhibitors with an IC₅₀ in the low micromolar range (4.4-14.6 μM). The chemical scaffolds of the three compounds were oxa-1-thia-4-aza-cyclopenta[b]naphthalene (KHG25229), phenyl-2,3-dihydro-isothiazole (KHG25386), and phenyl-pyrrolidine-3-carboxylic acid phenylamide (KHG25056). Further, molecular docking of the two most potent chemicals, KHG25229 and KHG25386, in Hi-AHAS yielded binding energies of −10.41 and −9.21 kcal/mol, respectively. The binding modes were consistent with inhibition mechanisms, as both chemicals oriented outside the active site. As the need for novel antibiotic classes to combat drug resistant bacteria increases, screening compounds that act against Hi-AHAS may assist in the identification of potential new anti-Hi drugs.     

A new classification of membrane protein crystals

Although being much smaller than the number of soluble proteins in the Protein Data Bank, the number of membrane proteins therein now approaches 700, and a statistical analysis becomes meaningful. Such an analysis showed that the conventional subdivision into monotopic, β-barrel and α-helical membrane proteins is appropriate but should be amended by a classification according to the detergent micelle structure in the crystal, which can be derived from the packing of the membrane-immersed parts of the proteins. The crystal packing density is specific for the three conventional types of membrane proteins and soluble proteins. It is also specific for three observed detergent arrangements that are micelle pockets, micelle filaments and micelle sheets, demonstrating that the detergent structure affects crystallization. The packing density distribution of crystals from integral membrane proteins has approximately the same shape as that of soluble proteins but is by a factor of two broader and shifted to lower density. It seems unlikely that the differences can be explained by a mere solvent expansion due to the required detergent. The crystallized membrane proteins were further analyzed with respect to protein mass, oligomerization and crystallographic asymmetric unit, space group, crystal ordering and symmetry. The results provide a new view on membrane proteins.     

Structure of the catalytic domain of glucuronoyl esterase Cip2 from Hypocrea jecorina

The structure of the catalytic domain of glucuronoyl esterase Cip2 from the fungus H. jecorina was determined at a resolution of 1.9 ?. This is the first structure of the newly established carbohydrate esterase family 15. The structure has revealed the residues Ser278-His411-Glu301 present in a triad arrangement as the active site. Ser278 is present in the novel consensus sequence GCSRXG reported earlier in the members of CE-15 family. The active site is exposed on the surface of the protein which has implications for the ability of the enzyme to hydrolyze ester bonds of large substrates. Efforts are underway to obtain crystals of Cip2_GE complexed with inhibitor and synthetic substrates. The activity of the glucuronoyl esterase could play a significant role in plant biomass degradation as its expected role is to separate the lignin from hemicelluloses by hydrolysis of the ester bond between 4-O-methyl-D-glucuronic acid moieties of glucuronoxylans and aromatic alcohols of lignin.     

Generation, characterization, and docking studies of DNA-hydrolyzing recombinant F(ab) antibodies

Previously we established a series of catalytic antibodies (catAbs) capable of hydrolyzing DNA prepared by hybridoma technology. A group of these catAbs exhibited high reactivity and substrate specificity. To determine the molecular basis for these catAbs, we cloned, sequenced, and expressed the variable regions of this group of antibodies as functional F(ab) fragments. The nucleotide and deduced amino acid sequences of the expressed light chain (Vκ) germline gene assignments confidently belonged to germline family Vκ1A, gene bb1.1 and GenBank accession number EF672207 while heavy chain variable region V(H) genes belonged to V(H) 1/V(H) J558, gene V130.3 and GenBank accession number EF672221. A well-established expression system based on the pARA7 vector was examined for its ability to produce catalytically active antibodies. Recombinant F(ab) (rF(ab) ) fragments were purified and their hydrolyzing activity was analyzed against supercoiled pUC19 plasmid DNA (scDNA). The study of rF(ab) provides important information about the potential catalytic activities of antibodies whose structure allows us to understand their basis of catalysis. Molecular surface analysis and docking studies were performed on the molecular interactions between the antibodies and poly(dA9), poly(dG9), poly(dT9), and poly(dC9) oligomers. Surface analysis identified the important sequence motifs at the binding sites, and different effects exerted by arginine and tyrosine residues at different positions in the light and heavy chains. This study demonstrates the potential usefulness of the protein DNA surrogate in the investigation of the origin of anti-DNA antibodies. These studies may define important features of DNA catAbs.     

Observation of hyperpositive non-linear effect in catalytic asymmetric organozinc additions to aldehydes

Asymmetric amplification is a phenomenon that is believed to play a key role in the emergence of homochirality in life. In asymmetric catalysis, theoretical and experimental models have been investigated to provide an understanding of how chiral amplification is possible, in particular based on non-linear effects. Interestingly, it has been proposed a quarter century ago that chiral catalysts, when not enantiopure might even be more enantioselective than their enantiopure counterparts. We show here that such hyperpositive non-linear effect in asymmetric catalysis is indeed possible. An in-depth study into the underlying mechanism was carried out, and the scheme we derive differs from the previous proposed models.     

Carnosic acid and carnosol inhibit adipocyte differentiation in mouse 3T3-L1 cells through induction of phase2 enzymes and activation of glutathione metabolism

In the previous studies, we reported that carnosic acid (CA) and carnosol (CS) originating from rosemary protected cortical neurons by activating the Keap1/Nrf2 pathway, which activation was initiated by S-alkylation of the critical cysteine thiol of the Keap1 protein by the “electrophilic” quinone-type of CA or CS. Here, we found that CA and CS inhibited the in vitro differentiation of mouse preadipocytes, 3T3-L1 cells, into adipocytes. In contrast, other physiologically-active and rosemary-originated compounds were completely negative. These actions seemed to be mediated by activation of the antioxidant-response element (ARE) and induction of phase2 enzymes. This estimation is justified by our present findings that only CA and CS among rosemary-originated compounds significantly activated the ARE and induced the phase2 enzymes. Next, we performed cDNA microarray analysis in order to identify the gene(s) responsible for these biological actions and found that phase2 enzymes (Gsta2, Gclc, Abcc4, and Abcc1), all of which are involved in the metabolism of glutathione (GSH), constituted 4 of the top 5 CA-induced genes. Furthermore, CA and CS, but not the other compounds tested, significantly increased the intracellular level of total GSH. Thus, we propose that the stimulation of GSH metabolism may be a critical step for the inhibition of adipocyte differentiation in 3T3-L1 cells and suggest that pro-electrophilic compounds such as CA and CS may be potential drugs against obesity-related diseases.     

Asymmetric reduction of β-ketoesters and chiral β-iminoesters: impact of a α-quaternary stereocenter

Diastereomeric reduction of nonactivated, hindered β-keto and chiral β-iminoesters are described. The influence of a α-stereocontrolled center on the efficiency and stereoselectivity of the reduction was studied. Reaction conditions were optimized to synthesize β-hydroxy- and β-aminoesters in good yields. In the case of chiral β-iminoesters, influence of matched/mismatched diastereomeric pairs has been assessed.     

Aralkyl selenoglycosides and related selenosugars in acetylated form activate protein phosphatase-1 and -2A

Aralkyl and aryl selenoglycosides as well as glycosyl selenocarboxylate derivatives were assayed on the activity of protein phosphatase-1 (PP1) and -2A (PP2A) catalytic subunits (PP1c and PP2Ac) in search of compounds for PP1c and PP2Ac effectors. The majority of tested selenoglycosides activated both PP1c and PP2Ac by ～2–4-fold in a phosphatase assay with phosphorylated myosin light chain substrate when the hydroxyl groups of the glycosyl moiety were acetylated, but they were without any effects in the non-acetylated forms. A peptide from the myosin phosphatase target subunit-1 (MYPT1^23–38) that included an RVxF PP1c-binding motif attenuated activation of PP1c by 2-Trifluoromethylbenzyl 2,3,4,6-tetra-O-acetyl-1-seleno-β-d-glucopyranoside (TFM-BASG) and 4-Bromobenzyl 2,3,4,6-tetra-O-acetyl-1-seleno-β-d-glucopyranoside (Br-BASG). MYPT1^23–38 stimulated PP2Ac and contributed to PP2Ac activation exerted by either Br-BASG or TFM-BASG. Br-BASG and TFM-BASG suppressed partially binding of PP1c to MYPT1 in surface plasmon resonance based binding experiments. Molecular docking predicted that the hydrophobic binding surfaces in PP1c for interaction with either the RVxF residues of PP1c-interactors or selenoglycosides are partially overlapped. Br-BASG and TFM-BASG caused a moderate increase in the phosphatase activity of HeLa cells in 1?h, and suppressed cell viability in 24?h incubations. In conclusion, our present study identified selenoglycosides as novel activators of PP1 and PP2A as well as provided insights into the structural background of their interactions establishing a molecular model for future design of more efficient phosphatase activator molecules.