title: Accelerating the Association of the Most Stable Protein-Ligand Complex by More than Two Orders of Magnitude.
abstract: The complex between the bacterial type 1 pilus subunit FimG and the peptide corresponding to the N-terminal extension (termed donor strand, Ds) of the partner subunit FimF (DsF) shows the strongest reported noncovalent molecular interaction, with a dissociation constant (KD ) of 1.5×10(-20)  m. However, the complex only exhibits a slow association rate of 330 m(-1)  s(-1) that limits technical applications, such as its use in affinity purification. Herein, a structure-based approach was used to design pairs of FimGt (a FimG variant lacking its own N-terminal extension) and DsF variants with enhanced electrostatic surface complementarity. Association of the best mutant FimGt/DsF pairs was accelerated by more than two orders of magnitude, while the dissociation rates and 3D structures of the improved complexes remained essentially unperturbed. A KD  value of 8.8×10(-22)  m was obtained for the best mutant complex, which is the lowest value reported to date for a protein/ligand complex.
authors.affiliation: Department of Biology, ETH Zurich, Otto-Stern-Weg 5, 8093, Zürich, Switzerland.
authors.forename: Christoph
authors.initials: C
authors.lastname: Giese
authors.affiliation: Department of Biology, ETH Zurich, Otto-Stern-Weg 5, 8093, Zürich, Switzerland.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Eras
authors.affiliation: Department of Biology, ETH Zurich, Otto-Stern-Weg 5, 8093, Zürich, Switzerland.
authors.forename: Anne
authors.initials: A
authors.lastname: Kern
authors.affiliation: Laboratory of Biomolecular Research, Paul Scherrer Institute, 5232, Villigen-PSI, Switzerland.
authors.forename: Martin A
authors.initials: MA
authors.lastname: Schärer
authors.affiliation: Laboratory of Biomolecular Research, Paul Scherrer Institute, 5232, Villigen-PSI, Switzerland.
authors.forename: Guido
authors.initials: G
authors.lastname: Capitani
authors.affiliation: Department of Biology, ETH Zurich, Otto-Stern-Weg 5, 8093, Zürich, Switzerland. rudi@mol.biol.ethz.ch.
authors.forename: Rudi
authors.initials: R
authors.lastname: Glockshuber
mesh_terms: D029968:Escherichia coli Proteins / Q000737:chemistry*; D036781:Fimbriae Proteins / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D015202:Protein Engineering; D055672:Static Electricity; D013499:Surface Properties
chemical_list: D029968:Escherichia coli Proteins; C521674:FimF protein, E coli; C529458:FimG protein, E coli; D008024:Ligands; D036781:Fimbriae Proteins
keywords: biophysics; electrostatic interactions; kinetics; protein engineering; protein-protein interactions