The specific interaction of a variety of modified hevein domains to chitooligosaccharides has been studied by NMR spectroscopy in order to assess the importance of aromatic-carbohydrate interactions for the molecular recognition of neutral sugars. These mutant AcAMP2-like peptides, which have 4-fluoro-phenylalanine, tryptophan, or 2-naphthylalanine at the key interacting positions, have been prepared by solid-phase synthesis. Their three-dimensional structures, when bound to the chitin-derived trisaccharide, have been deduced by NMR spectroscopy. By using DYANA and restrained molecular dynamics simulations with the AMBER 5.0 force field, the three-dimensional structures of the protein-sugar complexes have been obtained. The thermodynamic analysis of the interactions that occur upon complex formation have also been carried out. Regarding binding affinity, the obtained data have permitted the deduction that the larger the aromatic group, the higher the association constant and the binding enthalpy. In all cases, entropy opposes binding. In contrast, deactivation of the aromatic rings by attaching fluorine atoms decreases the binding affinity, with a concomitant decrease in enthalpy. The role of the chemical nature of the aromatic ring for establishing sugar contacts has been thus evaluated.

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The reactivity of individual C--H bonds in the methyl(trifluoromethyl)dioxirane TFDO oxygenation of stereogenic methylene groups in conformationally homogeneous monosubstituted cyclohexanes (2) has been determined. The unexpectedly high occurrence of O-atom insertion into C--H(ax) bonds suggests an in plane trajectory attack in the oxygenation while the diastereoselectivity of the reaction is qualitatively interpreted on the basis of the distinct hyperconjugative stabilization by the substituent of diastereomeric transition states due to long-range through bond interactions.

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Acyloin condensation between benzaldehyde and decarboxylated pyruvate results in the production of R-(-)-phenylacetylcarbinol, a chiral precursor of the drug ephedrine. Huge research efforts have been made to improve the conditions of this reaction and to avoid the generation of by-products. Recently, we reported the advantages of using whole cells of the yeast Debaryomyces etchellsii as biocatalysts for this purpose. In this work, a new strategy, which fulfills green chemistry principles, is proposed and is based on using seawater as a gentle solvent. We demonstrate that, under these conditions, several improvements can be made compared to employing freshwater: (1) the conversion of the starting material in (R)-PAC is higher and with a minimum production of by-products; (2) it is possible to increase at least twofold the benzaldehyde load in the reaction medium; (3) cells can maintain their activity after several recycling rounds, which makes (R)-PAC production an easy and economical process.

Yeast display is a powerful strategy that consists in exposing peptides or proteins of interest on the cell surface of this microorganism. Ever since initial experiments with this methodology were carried out, its scope has extended and many applications have been successfully developed in different science and technology fields. Several yeast display systems have been designed, which all involve introducting into yeast cells the gene fusions that contain the coding regions of a signal peptide, an anchor protein, to properly attach the target to the cell surface, and the protein of interest to be exposed, all of which are controlled by a strong promoter. In this work, we report the description of such elements for the alternative systems introduced by focusing particularly on anchor proteins. The comparisons made between them are included whenever possible, and the main advantages and inconveniences of each one are discussed. Despite the huge number of publications on yeast surface display and the revisions published to date, this topic has not yet been widely considered. Finally, given the growing interest in developing systems for non-Saccharomyces yeasts, the main strategies reported for some are also summarized.

The amino or carboxy-terminal regions of certain cell wall proteins are capable of anchoring foreign proteins or peptides on the cell wall of the yeast Saccharomyces cerevisiae. This possibility has resulted in the development of a methodology known as yeast display which has powerful applications in biotechnology, pharmacy, and medicine. This work describes the results of experiments in which the agglutinin Aga2p protein is used as an anchor and several leucine-based peptides have been introduced into its N-terminal or C-terminal position. We found that the sequence of these peptides can affect plasmid stability, growth kinetics, and levels of the fusion protein displayed, and we analyzed how the incubation conditions influence these parameters. Besides, we show that the introduction of these small peptides can modify the properties of cell cover; in particular, fusing five or ten leucine residues to the Aga2p protein results in greater hydrophobicity of the cell wall and also in increased resistance to the presence of the organic solvents acetonitrile and ethanol and to high salt concentrations. The introduction of the RLRLL sequence also results in higher resistance to the exposure of yeast cells to NaCl stress.

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