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1.  BION web server: predicting non-specifically bound surface ions 
Bioinformatics  2013;29(6):805-806.
Motivation: Ions are essential component of the cell and frequently are found bound to various macromolecules, in particular to proteins. A binding of an ion to a protein greatly affects protein’s biophysical characteristics and needs to be taken into account in any modeling approach. However, ion’s bounded positions cannot be easily revealed experimentally, especially if they are loosely bound to macromolecular surface.
Results: Here, we report a web server, the BION web server, which addresses the demand for tools of predicting surface bound ions, for which specific interactions are not crucial; thus, they are difficult to predict. The BION is easy to use web server that requires only coordinate file to be inputted, and the user is provided with various, but easy to navigate, options. The coordinate file with predicted bound ions is displayed on the output and is available for download.
Availability: http://compbio.clemson.edu/bion_server/
Supplementary information: Supplementary data are available at Bioinformatics online.
Contact: ealexov@clemson.edu
doi:10.1093/bioinformatics/btt032
PMCID: PMC3597141  PMID: 23380591
2.  Progress in developing Poisson-Boltzmann equation solvers 
Molecular based mathematical biology  2013;1:10.2478/mlbmb-2013-0002.
This review outlines the recent progress made in developing more accurate and efficient solutions to model electrostatics in systems comprised of bio-macromolecules and nano-objects, the last one referring to objects that do not have biological function themselves but nowadays are frequently used in biophysical and medical approaches in conjunction with bio-macromolecules. The problem of modeling macromolecular electrostatics is reviewed from two different angles: as a mathematical task provided the specific definition of the system to be modeled and as a physical problem aiming to better capture the phenomena occurring in the real experiments. In addition, specific attention is paid to methods to extend the capabilities of the existing solvers to model large systems toward applications of calculations of the electrostatic potential and energies in molecular motors, mitochondria complex, photosynthetic machinery and systems involving large nano-objects.
doi:10.2478/mlbmb-2013-0002
PMCID: PMC3816640  PMID: 24199185
Continuum electrostatics; Poisson-Boltzmann equation; numerical techniques; dielectric constant; molecular surface
3.  The Role of Protonation States in Ligand-Receptor Recognition and Binding 
Current pharmaceutical design  2013;19(23):4182-4190.
In this review we discuss the role of protonation states in receptor-ligand interactions, providing experimental evidences and computational predictions that complex formation may involve titratable groups with unusual pKa’s and that protonation states frequently change from unbound to bound states. These protonation changes result in proton uptake/release, which in turn causes the pH-dependence of the binding. Indeed, experimental data strongly suggests that almost any binding is pH-dependent and to be correctly modeled, the protonation states must be properly assigned prior to and after the binding. One may accurately predict the protonation states when provided with the structures of the unbound proteins and their complex; however, the modeling becomes much more complicated if the bound state has to be predicted in a docking protocol or if the structures of either bound or unbound receptor-ligand are not available. The major challenges that arise in these situations are the coupling between binding and protonation states, and the conformational changes induced by the binding and ionization states of titratable groups. In addition, any assessment of the protonation state, either before or after binding, must refer to the pH of binding, which is frequently unknown. Thus, even if the pKa’s of ionizable groups can be correctly assigned for both unbound and bound state, without knowing the experimental pH one cannot assign the corresponding protonation states, and consequently one cannot calculate the resulting proton uptake/release. It is pointed out, that while experimental pH may not be the physiological pH and binding may involve proton uptake/release, there is a tendency that the native receptor-ligand complexes have evolved toward specific either subcellular or tissue characteristic pH at which the proton uptake/release is either minimal or absent.
PMCID: PMC3625499  PMID: 23170880
protonation states; receptor-ligand interactions; pKa calculations; pH-dependence; electrostatics
4.  DelPhi: a comprehensive suite for DelPhi software and associated resources 
BMC Biophysics  2012;5:9.
Background
Accurate modeling of electrostatic potential and corresponding energies becomes increasingly important for understanding properties of biological macromolecules and their complexes. However, this is not an easy task due to the irregular shape of biological entities and the presence of water and mobile ions.
Results
Here we report a comprehensive suite for the well-known Poisson-Boltzmann solver, DelPhi, enriched with additional features to facilitate DelPhi usage. The suite allows for easy download of both DelPhi executable files and source code along with a makefile for local installations. The users can obtain the DelPhi manual and parameter files required for the corresponding investigation. Non-experienced researchers can download examples containing all necessary data to carry out DelPhi runs on a set of selected examples illustrating various DelPhi features and demonstrating DelPhi’s accuracy against analytical solutions.
Conclusions
DelPhi suite offers not only the DelPhi executable and sources files, examples and parameter files, but also provides links to third party developed resources either utilizing DelPhi or providing plugins for DelPhi. In addition, the users and developers are offered a forum to share ideas, resolve issues, report bugs and seek help with respect to the DelPhi package. The resource is available free of charge for academic users from URL: http://compbio.clemson.edu/DelPhi.php.
doi:10.1186/2046-1682-5-9
PMCID: PMC3463482  PMID: 22583952
DelPhi; Poisson-Boltzmann equation; Implicit solvation model; Electrostatics; Biological macromolecules; Software

Results 1-4 (4)