NMR Structures of Apo L. casei Dihydrofolate Reductase and Its Complexes with Trimethoprim and NADPH: Contributions to Positive Cooperative Binding from Ligand-Induced Refolding, Conformational Changes, and Interligand Hydrophobic Interactions

bS Supporting Information The enzyme dihydrofolate reductase (DHFR; 5,6,7,8-tetra-hydrofolate:NADPH oxidoreductase, EC 1.5.1.3) catalyzes the reduction of 7,8-dihydrofolate (DHF) to 5,6,7,8-tetrahydro-folate (THF) using NADPH as coenzyme.1 Since THF and its metabolites are precursors of purine and pyrimidine bases, the normal functioning of this enzyme is essential for proliferating cells. This makes DHFR an excellent target for antifolate drugs such as methotrexate (anticancer), pyrimethamine (antimalarial), and trimethoprim (antibacterial). Such agents act by inhibiting the enzyme in parasitic or malignant cells.1,2 The cooperative binding of ligands to DHFR plays an important role not only in the enzyme catalytic cycle (negative cooperativity in THF/ NADPH binding)3 but also in enzyme inhibition (positive cooperativity in antifolate/NADPH binding).4 The effects of positive cooperative binding in controlling enzyme inhibition ar

Interplay of histidine residues of the Alzheimer's disease Aβ peptide governs its Zn-induced oligomerization

Conformational changes of Aβ peptide result in its transformation from native monomeric state to the toxic soluble dimers, oligomers and insoluble aggregates that are hallmarks of Alzheimer’s disease (AD). Interactions of zinc ions with Aβ are mediated by the N-terminal Aβ(1–16) domain and appear to play a key role in AD progression. There is a range of results indicating that these interactions trigger the Aβ plaque formation. We have determined structure and functional characteristics of the metal binding domains derived from several Aβ variants and found that their zinc-induced oligomerization is governed by conformational changes in the minimal zinc binding site (6)HDSGYEVHH(14). The residue H6 and segment (11)EVHH(14), which are part of this site are crucial for formation of the two zinc-mediated interaction interfaces in Aβ. These structural determinants can be considered as promising targets for rational design of the AD-modifying drugs aimed at blocking pathological Aβ aggregation

Pyrrolidine/Azepane Ring Expansion via Intramolecular Ullmann-Type Annulation/Rearrangement Cascade: Synthesis of Highly Functionalized 1<i>H</i>‑Benzazepines

5-Arylpyrrolidine-2-carboxylates with an ortho-halogen substituent at 5-aryl and an electron-withdrawing group at the C4 position of the pyrrolidine ring were transformed into 1H-benzo­[b]­azepine-2-carboxylates under Cu­(I) promotion and microwave activation. Reaction promoter copper­(I) thiophene-2-carboxylate has been generated in situ in the reaction’s environment from Cu2O and thiophene-2-carboxylic acid. Functionalized 1H-benzo­[b]­azepine-2-carboxylates were obtained in racemic and optically active forms in 67–89% yields. Subsequent stereoselective 1,3-dipolar cycloaddition and an Ullmann-type annulation/rearrangement cascade (UARC) ensure a synthetic route to oligomeric optically active benzazepine species with a well-defined 3D-structure

Pyrrolidine/Azepane Ring Expansion via Intramolecular Ullmann-Type Annulation/Rearrangement Cascade: Synthesis of Highly Functionalized 1<i>H</i>‑Benzazepines

5-Arylpyrrolidine-2-carboxylates with an ortho-halogen substituent at 5-aryl and an electron-withdrawing group at the C4 position of the pyrrolidine ring were transformed into 1H-benzo­[b]­azepine-2-carboxylates under Cu­(I) promotion and microwave activation. Reaction promoter copper­(I) thiophene-2-carboxylate has been generated in situ in the reaction’s environment from Cu2O and thiophene-2-carboxylic acid. Functionalized 1H-benzo­[b]­azepine-2-carboxylates were obtained in racemic and optically active forms in 67–89% yields. Subsequent stereoselective 1,3-dipolar cycloaddition and an Ullmann-type annulation/rearrangement cascade (UARC) ensure a synthetic route to oligomeric optically active benzazepine species with a well-defined 3D-structure

Theoretical and NMR Conformational Studies of β-Proline Oligopeptides With Alternating Chirality of Pyrrolidine Units

Synthetic β-peptides are potential functional mimetics of native α-proteins. A recently developed, novel, synthetic approach provides an effective route to the broad group of β-proline oligomers with alternating patterns of stereogenic centers. Conformation of the pyrrolidine ring, Z/E isomerism of β-peptide bonds, and hindered rotation of the neighboring monomers determine the spatial structure of this group of β-proline oligopeptides. Preferences in their structural organization and corresponding thermodynamic properties are determined by NMR spectroscopy, restrained molecular dynamics and quantum mechanics. The studied β-proline oligopeptides exist in dimethyl sulfoxide solution in a limited number of conformers, with compatible energy of formation and different spatial organization. In the β-proline tetrapeptide with alternating chirality of composing pyrrolidine units, one of three peptide bonds may exist in an E configuration. For the alternating β-proline pentapeptide, the presence of an E configuration for at least of one β-peptide bond is mandatory. In this case, three peptide bonds synchronously change their configurations. Larger polypeptides may only exist in the presence of several E configurations of β-peptide bonds forming a wave-like extended structure