Chemistry

Sulfur K-edge X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations have been used to determine the electronic structures of two Mo bis-dithiolene complexes, [Mo(OSi)(bdt)2]1−  and [MoO(OSi)(bdt)2]1−, where OSi = [OSiPh2tBu]1−  and bdt = benzene-1,2-dithiolate(2−), that model the Mo(IV) and Mo(VI)═O states of the DMSO reductase family of molybdenum enzymes. These results show that the Mo(IV) complex undergoes metal-based oxidation unlike Mo tris-dithiolene complexes, indicating that the dithiolene ligands are behaving innocently. Experimentally validated calculations have been extended to model the oxo transfer reaction coordinate using dimethylsulfoxide (DMSO) as a substrate. The reaction proceeds through a transition state (TS1) to an intermediate with DMSO weakly bound, followed by a subsequent transition state (TS2) which is the largest barrier of the reaction. The factors that control the energies of these transition states, the nature of the oxo transfer process, and the role of the dithiolene ligand are discussed.

The similarities and differences in the fundamental coordination chemistry of molybdenum and tungsten mainly in physiological oxidation states MIV–VI are examined in relation to the properties of enzyme sites that catalyze oxygen atom transfer reactions. The comparative aspects of dithiolene complexes, which as synthetic analogues simulate structural and electronic features of these sites, are emphasized. Analogue reaction systems of enzymes

Improved rational drug design methods are needed to lower the cost and increase the success rate of drug discovery and development. Alchemical binding free energy calculations, one potential tool for rational design, have progressed rapidly over the past decade, but still fall short of providing robust tools for pharmaceutical engineering.

By employing thousands of PCs and new worldwide-distributed computing techniques, we have simulated in atomistic detail the folding of a fast-folding 36-residue α-helical protein from the villin headpiece. The total simulated time exceeds 300μs, orders of magnitude more than previous simulations of a molecule of this size.

Summary Unused CPU time on desktop computers could be put to good use, if distributed computing succeeds in capturing people's imagination. In their Perspective, Shirts and Pande describe existing distributed computing projects and recent efforts to overcome parallelization problems. This vast underused resource could raise biological and other scientific computation to fundamentally new predictive levels.

Recent hardware and software advances have enabled simulation studies of protein systems on biophysically relevant time scales, often revealing the need for improved force fields. Although early force field development was limited by the lack of direct comparisons between simulation and experiment, recent work from several laboratories has demonstrated direct calculation of NMR observables from protein simulations. Here, we quantitatively evaluate 11 recent molecular dynamics force fields in combination with 5 solvent models against a suite of 524 chemical shift and J coupling (3JHNHα, 3JHNCβ, 3JHαC′, 3JHNC′, and 3JHαN) measurements on dipeptides, tripeptides, tetra-alanine, and ubiquitin. Of the force fields examined (ff96, ff99, ff03, ff03*, ff03w, ff99sb*, ff99sb-ildn, ff99sb-ildn-phi, ff99sb-ildn-NMR, CHARMM27, and OPLS-AA), two force fields (ff99sb-ildn-phi, ff99sb-ildn-NMR) combining recent side chain and backbone torsion modifications achieved high accuracy in our benchmark. For the two optimal force fields, the calculation error is comparable to the uncertainty in the experimental comparison. This observation suggests that extracting additional force field improvements from NMR data may require increased accuracy in J coupling and chemical shift prediction. To further investigate the limitations of current force fields, we also consider conformational populations of dipeptides, which were recently estimated using vibrational spectroscopy.

Theoretical studies using simplified models of proteins have shed light on the general heteropolymeric aspects of the folding problem. Recent work has emphasized the statistical aspects of folding pathways. In particular, progress has been made in characterizing the ensemble of transition state conformations and elucidating the role of intermediates. These advances suggest a reconciliation between the new ensemble approaches and the classical view of a folding pathway.

Abstract. Despite their immense importance to cellular function, the precise mechanism by which chaperonins aid in the folding of other proteins remains unknown. Experimental evidence seems to imply that there is some diversity in how chaperonins interact with their substrates and this has led to a number of different models for chaperonin mechanism.

Abstract: When accounting for structural fluctuations or measurement errors, a single rigid structure may not be sufficient to represent a protein. One approach to solve this problem is to represent the possible conformations as a discrete set of observed conformations, an ensemble. In this work, we follow a different richer approach, and introduce a framework for estimating probability density functions in very high dimensions, and then apply it to represent ensembles of folded proteins.

Abstract We suggest a procedure to synthesize polymers with characteristics similar to those observed in globular proteins: renaturability and the existence of an" active site" capable of specifically recognizing a given target molecule. This procedure is investigated by computer simulation, which finds a yield of up to 65%. We believe that, in principle, this scheme can be realized in vitro. The applicability of this approach as a model of prebiotic synthesis in vivo is also discussed.

Understanding the mechanism of protein folding is a notori-ously difficult problem for both experiment and simulation (1, 2). In this issue of PNAS, through a combination of theory (Karanicolas and Brooks; ref. 3) and experiment (Nyguen et al.; ref. 4), progress toward the bridge between simulation and experiment is beautifully demonstrated. Indeed, lead by predictions made by Karanicolas and Brooks, Nyguen et al.

Abstract There are many unresolved questions regarding the role of water in protein folding. Does water merely induce hydrophobic forces, or does the discrete nature of water play a structural role in folding? Are the nonadditive aspects of water important in determining the folding mechanism? To help to address these questions, we have performed simulations of the folding of a model protein (BBA5) in explicit solvent.

Abstract Implementation of molecular dynamics (MD) calculations on novel architectures will vastly increase its power to calculate the physical properties of complex systems. Herein, we detail algorithmic advances developed to accelerate MD simulations on the Cell processor, a commodity processor found in PlayStation 3 (PS3).

The folding of proteins in confined spaces is a ubiquitous theme in biological and biomaterial applications, including folding in chaperones1 and pores, 2 nanotube-based drug delivery, 3 and cotranslational folding of nascent peptides in the ribosomal exit tunnel. 4 The role of confinement on peptide conformational equilibrium has thus gained much interest in recent years, and a natural first hypothesis to investigate is the role of confinement alone in protein conformational preferences.

LINGOs are a holographic measure of chemical similarity based on text comparison of SMILES strings. We present a new algorithm for calculating LINGO similarities amenable to parallelization on SIMD architectures (such as GPUs and vector units of modern CPUs). We show that it is nearly 3× as fast as existing algorithms on a CPU, and over 80× faster than existing methods when run on a GPU.

▪ Abstract Simulation of protein folding has come a long way in five years. Notably, new quantitative comparisons with experiments for small, rapidly folding proteins have become possible. As the only way to validate simulation methodology, this achievement marks a significant advance. Here, we detail these recent achievements and ask whether simulations have indeed rendered quantitative predictions in several areas, including protein folding kinetics, thermodynamics, and physics-based methods for structure prediction.