Large scale motions in a biosensor protein glucose oxidase: a combined approach by QENS, normal mode analysis, and molecular dynamics studies

Understanding the activity of glucose oxidase after exposure to organic solvents

Long-term stability of enzymes in organic solvents is one of the most challenging problems in modern biotechnology and chemical industries. However, the resistance of enzymes to organic solvents is not very well understood so far. Herein, the effects of apolar, chlorinated, and polar organic solvents on the activity and structure of glucose oxidase from Aspergillus niger were systemically investigated using spectrophotometric activity assay of this enzyme and absorption and chiroptical spectroscopy. Molecular dynamics simulations and correlation of the activity with properties of the organic solvents were employed to understand the effects of organic solvents on the enzyme. The experimental and theoretical results showed that apolar solvents reduce the enzyme activity because they facilitate its aggregation through inter-enzymatic salt bridges. Moreover, polar solvents strongly coordinate with amino acid residues in the glucose binding pocket and prevent binding of the substrates. We found that this enzyme is stable in pure apolar and chlorinated solvents and these solvents can be used for the functionalization of its residues. This work provides an in depth understanding at the molecular level of the impact of various pure organic solvents on the structure and dynamics of glucose oxidase and the regulation of its catalytic activity.

When Stiffness Matters: Mechanosensing in Heart Development and Disease

During embryonic morphogenesis, the heart undergoes a complex series of cellular phenotypic maturations (e.g., transition of myocytes from proliferative to quiescent or maturation of the contractile apparatus), and this involves stiffening of the extracellular matrix (ECM) acting in concert with morphogenetic signals. The maladaptive remodeling of the myocardium, one of the processes involved in determination of heart failure, also involves mechanical cues, with a progressive stiffening of the tissue that produces cellular mechanical damage, inflammation, and ultimately myocardial fibrosis. The assessment of the biomechanical dependence of the molecular machinery (in myocardial and non-myocardial cells) is therefore essential to contextualize the maturation of the cardiac tissue at early stages and understand its pathologic evolution in aging. Because systems to perform multiscale modeling of cellular and tissue mechanics have been developed, it appears particularly novel to design integrated mechano-molecular models of heart development and disease to be tested in ex vivo reconstituted cells/tissue-mimicking conditions. In the present contribution, we will discuss the latest implication of mechanosensing in heart development and pathology, describe the most recent models of cell/tissue mechanics, and delineate novel strategies to target the consequences of heart failure with personalized approaches based on tissue engineering and induced pluripotent stem cell (iPSC) technologies.

Tandem catalysis in multicomponent solvent-free biofluids

Enzymes are widely employed to reduce the environmental impact of chemical industries as biocatalysts improve productivity and offer high selectively under mild reaction conditions in a diverse range of chemical transformations. The poor stability of biomacromolecules under reaction conditions is often a critical bottleneck to their application. Protein engineering or immobilization onto solid substrates may remedy this limitation but, unfortunately, this is often at the expense of catalytic potency or substrate specificity. In this work, we show that the combinatorial approach of chemical modification and supramolecular nanoencapsulation can endow mechanistically diverse enzymes with apparent extremophilic behavior. A protein-polymer surfactant core-shell architecture facilitates construction of increasingly complex biofluids from individual biosynthetic components, each of which retain biological activity at hydration levels almost two orders of magnitude below solvation. The herein constructed multifunctional biofluids operate in tandem up to 150 °C and in the total absence of solvent under apparent diffusional mass-transport limitation. The biosynthetic promotion of extremophilic traits for enzymes with diverse catalytic motions and chemical functions highlights the extraordinary capacity for a viscous surfactant milieu to replace both hydration and bulk waters.

Signals of LOV1: a computer simulation study on the wildtype LOV1-domain of Chlamydomonas reinhardtii and its mutants

Phototropins are photoreceptors regulating the blue-light response in plants and bacteria. They consist of two LOV (light oxygen voltage sensitive) domains each containing a non-covalently bound flavin-mononucleotide (FMN) chromophore, which are connected to a serine/threonine-kinase. Upon illumination, the LOV-domains undergo conformational changes, triggering a signal cascade in the organism through kinase activation. Here, we present results from molecular dynamics simulations in which we investigate the signal transduction pathway of the wildtype LOV1-domain of Chlamydomonas reinhardtii and a methyl-mercaptan (MM) adduct of its Cys57Gly-mutant at the molecular level. In particular, we analyzed the effect of covalent-bond formation between the reactive cysteine Cys57 and the FMN-reaction center, as well as the subsequent charge redistribution, on the spatio-dynamical behavior of the LOV1-domain. We compare the calculation results with experimental data and demonstrate that these adduct state characteristics have an important influence on the response of this photosensor. The light-induced changes implicate primarily an alteration of the surface charge distribution through rearrangement of the highly flexible Cα-, Dα- and Eα-helices including the Glu51-Lys91-salt bridge on the hydrophilic side of the protein domain and a β-sheet tightening process via coupling of the Aβ- and Bβ-strands. Our findings confirm the aptitude of the LOV1-domain to function as a dimerization partner, allowing the green alga to adapt its reproduction and growth speed to the environmental conditions.