Enzyme and Cell Engineering - Molecular Recognition and Biocatalysis

Carnosine is accumulated in the animal tissue particularly at high concentrations in the muscle tissue. The antioxidant mechanism of carnosine has been attributed to its chelation of metal ions, its superoxide dismutase (SOD)-like activity and its ability to scavenge reactive oxygen species (ROS) and other free radicals. In this chapter, carnosine constitutes an undeniable challenging substrate for chemical or enzymatic modifications leading to pharmaceutical, cosmetic and nutraceutical applications. The main limitation on therapeutic use of carnosine is due to increased oxidative stress associated with the hydrolysis by the specific dipeptidase carnosinase. Several attempts have been made to overcome this drawback. Several carnosine derivatives with saccharides, such as β-cyclodextrin and trehalose have been synthesised. All these compounds are able to scavenge hydroxyl radicals, and their copper (II) complexes exhibit SOD activity. Carnosine exhibits many biological activities and is a very promising therapeutic molecule.

The author wishes to make the following erratum to this paper [...]

La biomasse lignocellulosique (BLC), composée des déchets végétaux agricoles et/ou forestiers, représente une ressource renouvelable prometteuse pour la production de bioéthanol de deuxième génération et faire face à l'épuisement des énergies fossiles. Le procédé de valorisation de la BLC appliqué ici comprend une étape de prétraitement par deux liquides ioniques (LI) hydrophiles dérivés d'imidazolium, le 1-éthyl-3-méthylimidazolium acétate [Emim][OAc] et le 1-éthyl-3-méthylimidazolium méthylphosphonate [Emim][MeO(H)PO2], puis une hydrolyse enzymatique par des cellulases de Trichoderma reesei et des xylanases de Trichoderma longibrachiatum, suivie d'une étape de fermentation éthanolique microbienne testée sur quatre espèces de levures: Saccharomyces cerevisiae, Kluyveromyces marxianus, Scheffersomyces shehatae et Scheffersomyces stipitis. Deux BLC réelles ont été étudiées : le saule blanc (résidu forestier) et le son de blé désamidonné (résidu agricole). Les résultats ont montré que le prétraitement des BLC aux LI à 35°C permet une augmentation de la digestibilité enzymatique des polysaccharides (rendements en glucose jusqu'à +56,7% et rendements en xylose jusqu'à +31,1%) par rapport au contrôle sans prétraitement. De plus, la performance des procédés de fermentation éthanolique est améliorée d'un facteur 1,3 à 4,6 en fonction du substrat étudié et de l'espèce de levure utilisée. Ainsi, les LI sont des solvants prometteurs pour le prétraitement de la (ligno)cellulose à basse température permettant une hausse des rendements d'hydrolyse enzymatique et de production éthanolique

Molecularly imprinted polymers (MIPs) are receptor-like biomimetic materials. They are cross-linked polymers synthesized in the presence of a molecular template, which induces three-dimensional binding sites in the polymer that are complementary to the template in size, shape and position of chemical groups. In the present work, they were used to recognize and immobilize photosynthetic bacteria on polymeric scaffolds. Due to the challenges of imprinting whole bacteria, cell surface proteins were more reasonable candidates for cell recognition. Thus, the Slr1270 protein from the cyanobacterium Synechocystis sp. PCC 6803 was chosen as the target protein for imprinting using protein structure data banks and bioinformatics tools. Two epitope sequences were selected and validated by an in silico rational approach, where after a template peptide was chemically synthesized. MIPs targeting the Slr1270 peptide epitopes were then synthesized by a solid-phase approach. N-propylacrylamide was incorporated as the main monomer into the polymerization mixture to generate thermoresponsive MIPs that feature a lower critical solution temperature around 25ºC. The MIP nanogels were then characterized using dynamic light scattering and scanning electron microscopy. The resulting MIPs showed the ability to recognize and bind their template epitope peptides as well as the whole bacterium as shown by fluorescent equilibrium binding assays, flow cytometry and fluorescence microscopy. Various approaches were developed for interfacing the MIPs with the nanocellulose matrix, based on physisorption and chemisorption. To measure the interactions between cells and the nanocellulose matrix, various techniques were employed, including QCM-D, electron and light microscopy techniques.

Les rhamnolipides produits par Pseudomonas aeruginosa sont des glycolipides ayant des propriétés élicitrices des réactions de défense de la vigne et d'Arabidopsis thaliana dont le mode de perception est inconnu. En tant que composés amphiphiles, uneinteraction avec la membrane plasmique a été proposée. Au niveau fondamental, il est démontré ici par une approche de biophysique utilisant la RMN du solide et des simulations de dynamique moléculaire in silico, que le caractère amphiphile des RLs favorise leur insertion au sein de modèles lipidiques de membranes de plantes, qui ne sont pas déstabilisés par leur présence. De plus il a été observé, par la réalisation de puces à ADN sur A. thaliana, que la perception de ces composés induisait une reprogrammation transcriptionnelle précoce de grande ampleur. En vue de démontrer l'intérêt agronomique des RLs pour la protection d'une plante de grande culture, leur activité sur le colza (Brassica napus) a également été étudiée. Des marqueurs caractéristiques de la mise en place des réponses de défense ont été observés, ainsi qu'un effet de protection detissus foliaires contre le pathogène B. cinerea, ce qui renforce le potentiel des RLs comme agents de biocontrôle pour la protection des Brassicacées

A general procedure for the formation of solid-supported artificial membranes containing transmembrane proteins is reported. The main objective was to directly use the pool of proteins of the native biomembrane (here the inner membrane from mitochondria of human carcinogenic hepatic cells) and to avoid purification steps with detergent. Proteoliposomes of phospholipid-enriched inner membranes from mitochondria were tethered and fused onto a tailored surface via a streptavidin link. The failure of some preliminary experiments on membrane formation was attributed to strong nonspecific interactions between the solid surface and the protuberant hydrophilic parts of the transmembrane complexes. The correct loading of uniform membranes was performed after optimization of a tailored surface, covered with a grafted short-chain poly(ethylene glycol), so that nonspecific interactions are reduced. Step-by-step assembly of the structure and triggered fusion of the immobilized proteoliposomes were monitored by surface plasmon resonance and fluorescence photobleaching recovery, respectively. The long-range lateral diffusion coefficient (at 22 °C) for a fluorescent lipid varies from 2.5 10-8 cm2 s-1 for a tethered lipid bilayer without protein to 10-9 cm2 s-1 for a tethered membrane containing the transmembrane proteins of the respiratory chain at a protein area fraction of about 15%. The decrease in the diffusion coefficient in the tethered membrane with increase in protein area fraction was too pronounced to be fully explained by the theoretical models of obstructed lateral diffusion. Covalent tethering links with the solid are certainly involved in the decrease of the overall lateral mobility of the components in the supported membrane at the highest protein-to-lipid ratios.