Allosteric regulation of the nickel-responsive NikR transcription factor from Helicobacter pylori.

Nickel is essential for the survival of the pathogenic bacteria Helicobacter pylori in the fluctuating pH of the human stomach. Due to its inherent toxicity and limited availability, nickel homeostasis is maintained through a network of pathways that are coordinated by the nickel-responsive transcription factor NikR. Nickel binding to H.

Detergent- and phospholipid-based reconstitution systems have differential effects on constitutive activity of G-protein-coupled receptors.

A hallmark of G-protein-coupled receptors (GPCRs) is the conversion of external stimuli into specific cellular responses. In this tightly-regulated process, extracellular ligand binding by GPCRs promotes specific conformational changes within the seven transmembrane helices, leading to the coupling and activation of intracellular "transducer" proteins, such as heterotrimeric G proteins. Much of our understanding of the molecular mechanisms that govern GPCR activation is derived from experiments with purified receptors reconstituted in detergent micelles.

Mechanistic insights into allosteric regulation of the A adenosine G protein-coupled receptor by physiological cations.

Cations play key roles in regulating G-protein-coupled receptors (GPCRs), although their mechanisms are poorly understood. Here, F NMR is used to delineate the effects of cations on functional states of the adenosine A GPCR. While Na reinforces an inactive ensemble and a partial-agonist stabilized state, Ca and Mg shift the equilibrium toward active states.

Site-Specific Labeling of Protein Lysine Residues and N-Terminal Amino Groups with Indoles and Indole-Derivatives.

Indoles and indole-derivatives can be used to site-specifically label proteins on lysine and N-terminal amino groups under mild, nondenaturing reaction conditions. Hen egg white lysozyme (HEWL) and α-lactalbumin were labeled with indole, fluoroindole, or fluoroindole-2-carboxylate via electrophilic aromatic substitutions to lysine side chain Nε- and N-terminal amino imines, formed in situ in the presence of formaldehyde. The reaction is highly site-selective, easily controlled by temperature, and does not eliminate the native charge of the protein, unlike many other common lysine-specific labeling strategies.

Mechanistic investigation of aziridine aldehyde-driven peptide macrocyclization: the imidoanhydride pathway.

Aziridine aldehyde dimers, peptides, and isocyanides participate in a multicomponent reaction to yield peptide macrocycles. We have investigated the selectivity and kinetics of this process and performed a detailed analysis of its chemoselectivity. While the reactants encompass all of the elements of the traditional Ugi four-component condensation, there is a significant deviation from the previously proposed mechanism.

Temperature-Invariant Aqueous Microgels as Hosts for Biomacromolecules.

Immobilization of enzymes on solid supports has been widely used to improve enzyme recycling, enzyme stability, and performance. We are interested in using aqueous microgels (colloidal hydrogels) as carriers for enzymes used in high-temperature reactions. These microgels should maintain their volume and colloidal stability in aqueous media up to 100 °C to serve as thermo-stable supports for enzymes.

Ion-Mediated Gelation of Aqueous Suspensions of Cellulose Nanocrystals.

Nanofibrillar hydrogels are an important class of biomaterials with applications as catalytic scaffolds, artificial extracellular matrixes, coatings, and drug delivery materials. In the present work, we report the results of a comprehensive study of nanofibrillar hydrogels formed by cellulose nanocrystals (CNCs) in the presence of cations with various charge numbers and ionic radii. We examined sol-gel transitions in aqueous CNC suspensions and the rheological and structural properties of the CNC hydrogels.