Site-Specific Identification of Lysine Acetylation Stoichiometries in Mammalian Cells.

Functional characterization of the lysine acetylation pathway requires quantitative measurement of the modification abundance at the stoichiometry level. Here, we developed a systematic workflow for global untargeted identification of site-specific Lys acetylation stoichiometries in mammalian cells. Our strategy includes an optimized protocol for in vitro chemical labeling of unmodified lysine with stable isotope-encoded acetyl-NHS ester, deep proteomic profiling with a high resolution mass spectrometer, and a new software tool for quantitative analysis and stoichiometry determination.

RevErbα preferentially deforms DNA by induced fit.

Using free-energy simulations, we have shown that RevErbα-induced DNA deformation preferentially occurs by induced fit rather than by conformational selection, even though the DNA is only slightly distorted in the complex. Our study shows that information on the sequence of binding events is needed to establish whether conformational selection or induced fit is operative, and that the presence of multiple apo-state structures might not be enough to distinguish between these binding models

Free energy simulation of helical transitions.

An umbrella sampling method for the calculation of free energies for helical transitions is presented. The method biases structures toward helices of a desired radius and pitch. Although computationally complex, the method has negligible overhead in actual applications.

In silico prediction of the 3D structure of trimeric asialoglycoprotein receptor bound to triantennary oligosaccharide.

In this study, we present a general-purpose methodology for deriving the three-dimensional (3D) arrangement of multivalent transmembrane complexes in the presence of their ligands. Specifically, we predict the most likely families of structures of the experimentally intractable trimeric asialoglycoprotein receptor (ASGP-R), which consists of human hepatic subunits (two subunits of H1 and one subunit of H2), bound to a triantennary oligosaccharide (TA). Because of the complex nature of this multivalent type-II transmembrane hetero-oligomeric receptor, structural studies have to date been unable to provide the 3D arrangement of these subunits.

When sugars get wet. A comprehensive study of the behavior of water on the surface of oligosaccharides.

In this article, we characterize the behavior of water on the surface of a diverse group of carbohydrates and attempt to determine the role of saccharide size, linkage, and branching as well as secondary structure on the dynamics and structure of water at the surface. In order to better understand the similarities and differences in the behavior of the solvent on the carbohydrate surface, we explore residence times, rotational correlation functions, local solvent occupancy numbers, and diffusivities. We find that due to the differences in secondary structure water residence times are longer and translational and rotational dynamics are retarded when in contact with wide helices and branched sugars.

Rationalization of the difference in lifetime of two covalent sialosyl-enzyme intermediates of Trypanosoma rangeli sialidase.

The difference in lifetime with respect to hydrolysis of two covalent syalosyl-enzyme intermediates of two difluorinated sialic acid analogues ( 1 and 2) bound to Trypanosoma rangeli sialidase is rationalized based on quantum mechanical calculations. The two intermediates differ only in a single functional group, acetamide in the sialidase- 1 complex and hydroxyl in the sialidase- 2 complex. It is shown that the acetamide group, which is also present in the natural substrate, increases the pKa of a catalytic base (Asp60) through electrostatic repulsion with the carbonyl oxygen on the ligand.

Diffusion and residence time of hydrogen peroxide and water in crowded protein environments.

Reactive oxygen species (ROS) have important functions in cell signaling and, when present at overly high levels, may cause oxidation of important biological molecules. Kinetic models to study diffusion of ROS inside of mitochondria often assume dynamics similar to that in solution. However, it is well-known that separation of proteins in the cytosol or inside of mitochondria, where ROS are most predominant, can be smaller than 1 nm.