title: Contrasting factors on the kinetic path to protein complex formation diminish the effects of crowding agents.
abstract: The crowded environment of cells poses a challenge for rapid protein-protein association. Yet, it has been established that the rates of association are similar in crowded and in dilute solutions. Here we probe the pathway leading to fast association between TEM1 β-lactamase and its inhibitor protein BLIP in crowded solutions. We show that the affinity of the encounter complex, the rate of final complex formation, and the structure of the transition state are similar in crowded solutions and in buffer. The experimental results were reproduced by calculations based on the transient-complex theory for protein association. Both experiments and calculations suggest that while crowding agents decrease the diffusion constant of the associating proteins, they also induce an effective excluded-volume attraction between them. The combination of the two opposing effects thus results in nearly identical overall association rates in diluted and crowded solutions.
authors.affiliation: Department of Biological Chemistry, Weizmann Institute of Science, Rehovot, Israel.
authors.forename: Yael
authors.initials: Y
authors.lastname: Phillip
authors.forename: Michal
authors.initials: M
authors.lastname: Harel
authors.forename: Ruth
authors.initials: R
authors.lastname: Khait
authors.forename: Sanbo
authors.initials: S
authors.lastname: Qin
authors.forename: Huan-Xiang
authors.initials: HX
authors.lastname: Zhou
authors.forename: Gideon
authors.initials: G
authors.lastname: Schreiber
mesh_terms: D002021:Buffers; D003911:Dextrans / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000378:metabolism* / Q000494:pharmacology; D007700:Kinetics; D008958:Models, Molecular; D009154:Mutation; D011092:Polyethylene Glycols / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D011487:Protein Conformation; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases / Q000235:genetics / Q000378:metabolism*
chemical_list: D002021:Buffers; D003911:Dextrans; D004791:Enzyme Inhibitors; D065093:beta-Lactamase Inhibitors; D011092:Polyethylene Glycols; D001618:beta-Lactamases