title: Dynamics of protein-protein encounter: a Langevin equation approach with reaction patches.
abstract: We study the formation of protein-protein encounter complexes with a Langevin equation approach that considers direct, steric, and thermal forces. As three model systems with distinctly different properties we consider the pairs barnase:barstar, cytochrome c-cytochrome c peroxidase, and p53:MDM2. In each case, proteins are modeled either as spherical particles, as dipolar spheres, or as collection of several small beads with one dipole. Spherical reaction patches are placed on the model proteins according to the known experimental structures of the protein complexes. In the computer simulations, concentration is varied by changing box size. Encounter is defined as overlap of the reaction patches and the corresponding first passage times are recorded together with the number of unsuccessful contacts before encounter. We find that encounter frequency scales linearly with protein concentration, thus proving that our microscopic model results in a well-defined macroscopic encounter rate. The number of unsuccessful contacts before encounter decreases with increasing encounter rate and ranges from 20 to 9000. For all three models, encounter rates are obtained within one order of magnitude of the experimentally measured association rates. Electrostatic steering enhances association up to 50-fold. If diffusional encounter is dominant (p53:MDM2) or similarly important as electrostatic steering (barnase:barstar), then encounter rate decreases with decreasing patch radius. More detailed modeling of protein shapes decreases encounter rates by 5%-95%. Our study shows how generic principles of protein-protein association are modulated by molecular features of the systems under consideration. Moreover it allows us to assess different coarse-graining strategies for the future modeling of the dynamics of large protein complexes.
authors.affiliation: University of Heidelberg, Bioquant 0013, Im Neuenheimer Feld 267, 69120 Heidelberg, Germany.
authors.forename: Jakob
authors.initials: J
authors.lastname: Schluttig
authors.forename: Denitsa
authors.initials: D
authors.lastname: Alamanova
authors.forename: Volkhard
authors.initials: V
authors.lastname: Helms
authors.forename: Ulrich S
authors.initials: US
authors.lastname: Schwarz
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D045304:Cytochromes c / Q000737:chemistry / Q000378:metabolism; D008956:Models, Chemical; D008958:Models, Molecular; D009195:Peroxidase / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D051736:Proto-Oncogene Proteins c-mdm2 / Q000737:chemistry / Q000378:metabolism; D012260:Ribonucleases / Q000737:chemistry / Q000378:metabolism; D013997:Time Factors; D016159:Tumor Suppressor Protein p53 / Q000737:chemistry / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D016159:Tumor Suppressor Protein p53; C057438:barstar protein, Bacillus amyloliquefaciens; D045304:Cytochromes c; D009195:Peroxidase; D051736:Proto-Oncogene Proteins c-mdm2; D012260:Ribonucleases; C019760:Bacillus amyloliquefaciens ribonuclease