title: PHEPS: web-based pH-dependent Protein Electrostatics Server.
abstract: PHEPS (pH-dependent Protein Electrostatics Server) is a web service for fast prediction and experiment planning support, as well as for correlation and analysis of experimentally obtained results, reflecting charge-dependent phenomena in globular proteins. Its implementation is based on long-term experience (PHEI package) and the need to explain measured physicochemical characteristics at the level of protein atomic structure. The approach is semi-empirical and based on a mean field scheme for description and evaluation of global and local pH-dependent electrostatic properties: protein proton binding; ionic sites proton population; free energy electrostatic term; ionic groups proton affinities (pK(a,i)) and their Coulomb interaction with whole charge multipole; electrostatic potential of whole molecule at fixed pH and pH-dependent local electrostatic potentials at user-defined set of points. The speed of calculation is based on fast determination of distance-dependent pair charge-charge interactions as empirical three exponential function that covers charge-charge, charge-dipole and dipole-dipole contributions. After atomic coordinates input, all standard parameters are used as defaults to facilitate non-experienced users. Special attention was given to interactive addition of non-polypeptide charges, extra ionizable groups with intrinsic pK(a)s or fixed ions. The output information is given as plain-text, readable by 'RasMol', 'Origin' and the like. The PHEPS server is accessible at http://pheps.orgchm.bas.bg/home.html.
authors.affiliation: Biophysical Chemistry Group, Institute of Organic Chemistry, Bulgarian Academy of Sciences, Sofia-1113, Bulgaria.
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Kantardjiev
authors.forename: Boris P
authors.initials: BP
authors.lastname: Atanasov
mesh_terms: D006863:Hydrogen-Ion Concentration; D020407:Internet; D007477:Ions / Q000737:chemistry; D011506:Proteins / Q000737:chemistry*; D011522:Protons; D012984:Software; D055672:Static Electricity
chemical_list: D007477:Ions; D011506:Proteins; D011522:Protons