Margaret M. Hurley

Simple one-electron quantum capping potentials for use in hybrid QM/MM studies of biological molecules

Calculations demonstrate that with a minor modification conventional ab initio effective potentials can be employed in place of link atoms to truncate quantum regions in hybrid quantum mechanics/molecular mechanics calculations. Simple quantum capping potentials are formed by replacing excess valence electrons in conventional effective potentials by spherical shielding and Pauli terms chosen to duplicate all-electron molecular structures and charge distributions. Tests involving truncated histidine show errors in charge and protonation energy to be reduced as compared to the link atom approach. Because of the use of conventional effective potential expansions, this approach can be implemented with minimal or no program modifications. Indeed, in its simplest form it requires the addition of only a single Gaussian and adjustable parameter to a conventional effective potential expansion. The parametrization requires little effective potential expertise or effort.

Photocurrent Generation from Surface Assembled Photosystem I on Alkanethiol Modified Electrodes

Photosystem I (PSI) is a key component of oxygenic photosynthetic electron transport because of its light-induced electron transfer to the soluble electron acceptor ferredoxin. This work demonstrates the incorporation of surface assembled cyanobacterial trimeric PSI complexes into a biohybrid system for light-driven current generation. Specifically, this work demonstrates the improved assembly of PSI via electrophoretic deposition, with controllable surface assembled PSI density, on different self-assembled alkanethiol monolayers. Using artificial electron donors and acceptors (Os(bpy)(2)Cl(2) and methyl viologen) we demonstrate photocurrent generation from a single PSI layer, which remains photoactive for at least three hours of intermittent illumination. Photoelectrochemical comparison of the biohybrid systems assembled from different alkanethiols (hexanethiol, aminohexanethiol, mercaptohexanol, and mercaptohexanoic acid) reveals that the PSI generated photocurrent is enhanced by almost 5 times on negatively charged SAM surfaces as compared to positively charged surfaces. These results are discussed in light of how PSI is oriented upon electrodeposition on a SAM.

Acetylcholinesterase: Molecular Modeling with the Whole Toolkit

Molecular modeling efforts aimed at probing the structure, function and inhibition of the acetylcholinesterase enzyme have abounded in the last decade, largely because of the systems importance to medical conditions such as myasthenia gravis, Alzheimers disease and Parkinsons disease, and well as its famous toxicological susceptibility to nerve agents. The complexity inherent in such a system with multiple complementary binding sites, critical dynamic effects and intricate mechanisms for enzymatic function and covalent inhibition, has led to an impressively diverse selection of simulation techniques being applied to the system, including quantum chemical mechanistic studies, molecular docking prediction of noncovalent complexes and their associated binding free energies, molecular dynamics conformational analysis and transport kinetics prediction, and quantitative structure activity relationship modeling to tie salient details together into a coherent predictive tool. Effective drug and prophylaxis design strategies for a complex target like this requires some understanding and appreciation for all of the above methods, thus it makes an excellent case study for multi-tiered pharmaceutical modeling. This paper reviews a sample of the more important studies on acetylcholinesterase and helps to elucidate their interdependencies. Potential future directions are introduced based on the special methodological needs of the acetylcholinesterase system and on emerging trends in molecular modeling.

Genetically engineered peptides for inorganics: study of an unconstrained bacterial display technology and bulk aluminum alloy.

The first-ever peptide biomaterial discovery using an unconstrained engineered bacterial display technology is reported. Using this approach, we have developed genetically engineered peptide binders for a bulk aluminum alloy and use molecular dynamics simulation of peptide conformational fluctuations to demonstrate sequence-dependent, structure-function relationships for metal and metal oxide interactions.

Development of Bacterial Display Peptides for use in Biosensing Applications

Recent advances in synthetic library engineering continue to show promise for the rapid production of reagent technology in response to biological threats. A synthetic library of peptide mutants built off a bacterial host offers a convenient means to link the peptide sequence, (i.e., identity of individual library members) with the desired molecular recognition traits, but also allows for a relatively simple protocol, amenable to automation. An improved understanding of the mechanisms of recognition and control of synthetic reagent isolation and evolution remain critical to success. In this paper, we describe our approach to development of peptide affinity reagents based on peptide bacterial display technology with improved control of binding interactions for stringent evolution of reagent candidates, and tailored performance capabilities. There are four key elements to the peptide affinity reagent program including: (1) the diverse bacterial library technology, (2) advanced reagent screening amenable to laboratory automation and control, (3) iterative characterization and feedback on both affinity and specificity of the molecular interactions, and (3) integrated multiscale computational prescreening of candidate peptide ligands including in silico prediction of improved binding performance. Specific results on peptides binders to Protective Antigen (PA) protein of Bacillus anthracis and Staphylococcal Enterotoxin B (SEB) will be presented. Recent highlights of on cell vs. off-cell affinity behavior and correlation of the results with advanced docking simulations on the protein-peptide system(s) are included. The potential of this technology and approach to enable rapid development of a new affinity reagent with unprecedented speed (less than one week) would allow for rapid response to new and constantly emerging threats.

Phosphoketolase flux in Clostridium acetobutylicum during growth on L-arabinose

Clostridium acetobutylicums metabolic pathways have been studied for decades due to its metabolic diversity and industrial value, yet many details of its metabolism continue to emerge. The flux through the recently discovered pentose phosphoketolase pathway (PKP) in C. acetobutylicum has been determined for growth on xylose but transcriptional analysis indicated the pathway may have a greater contribution to arabinose metabolism. To elucidate the role of xylulose-5-phosphate/fructose-6-phosphate phosphoketolase (XFP), and the PKP in C. acetobutylicum, experimental and computational metabolic isotope analyses were performed under growth conditions of glucose or varying concentrations of xylose and arabinose. A positional bias in labelling between carbons 2 and 4 of butyrate was found and posited to be due to an enzyme isotope effect of the thiolase enzyme. A correction for the positional bias was applied, which resulted in reduction of residual error. Comparisons between model solutions with low residual error indicated flux through each of the two XFP reactions was variable, while the combined flux of the reactions remained relatively constant. PKP utilization increased with increasing xylose concentration and this trend was further pronounced during growth on arabinose. Mutation of the gene encoding XFP almost completely abolished flux through the PKP during growth on arabinose and resulted in decreased acetate/butyrate ratios. Greater flux through the PKP during growth on arabinose when compared with xylose indicated the pathways primary role in C. acetobutylicum is arabinose metabolism.

XPairIt Docking Protocol for peptide docking and analysis

The mechanics of peptide–protein docking has long been an area of intense interest to the computational community. Here we discuss an improved docking protocol named XPairIt which uses a multitier approach, combining the PyRosetta docking software with the NAMD molecular dynamics package through a biomolecular simulation programming interface written in Python. This protocol is designed for systems where no a priori information of ligand structure (beyond sequence) or binding location is known. It provides for efficient incorporation of both ligand and target flexibility, is HPC-ready and is easily extensible for use of custom code. We apply this protocol to a set of 11 test cases drawn from benchmarking databases and from previously published studies for direct comparison with existing protocols. Strengths, weaknesses and areas of improvement are discussed.

In silico design of smart binders to anthrax PA

The development of smart peptide binders requires an understanding of the fundamental mechanisms of recognition which has remained an elusive grail of the research community for decades. Recent advances in automated discovery and synthetic library science provide a wealth of information to probe fundamental details of binding and facilitate the development of improved models for a priori prediction of affinity and specificity. Here we present the modeling portion of an iterative experimental/computational study to produce high affinity peptide binders to the Protective Antigen (PA) of Bacillus anthracis. The result is a general usage, HPC-oriented, python-based toolkit based upon powerful third-party freeware, which is designed to provide a better understanding of peptide-protein interactions and ultimately predict and measure new smart peptide binder candidates. We present an improved simulation protocol with flexible peptide docking to the Anthrax Protective Antigen, reported within the context of experimental data presented in a companion work.

Environmental Fate and Transport of Energetic Materials

This project strives to improve our understanding of the environmental behavior of energetic materials (EM). A thorough understanding of how these EM interact with soil and water is expected to ultimately lead to improved remediation strategies. The immediate goals of the project are to predict a priori the chemical interactions of energetic materials with model soils; and to predict a priori the decomposition reactions of EM and resultant breakdown products. Adsorption research will involve periodic density functional theory (DFT) calculations, using plane-wave/pseudopotential codes. Decomposition studies will use the Specular Reflection Isopotential Searching algorithm of Irikura et al.

Structural analysis of Clostridium acetobutylicum ATCC 824 glycoside hydrolase from CAZy family GH105

The crystal structure of the protein product of the C. acetobutylicum ATCC 824 gene CA_C0359 is structurally similar to YteR, an unsaturated rhamnogalacturonyl hydrolase from B. subtilis strain 168. Substrate modeling and electrostatic studies of the active site of the structure of CA_C0359 suggests that the protein can now be considered to be part of CAZy glycoside hydrolase family 105.