title: Concentration-Induced Association in a Protein System Caused by a Highly Directional Patch Attraction.
abstract: Self-association of the protein lactoferrin is studied in solution using small-angle X-ray scattering techniques. Effective static structure factors have been shown to exhibit either a monotonic or a nonmonotonic dependence on protein concentration in the small wavevector limit, depending on salt concentration. The behavior correlates with a nonmonotonic dependence of the second virial coefficient on salt concentration, such that a maximum appears in the structure factor at a low protein concentration when the second virial coefficient is negative and close to a minimum. The results are interpreted in terms of an integral equation theory with explicit dimers, formulated by Wertheim, which provides a consistent framework able to explain the behavior in terms of a monomer-dimer equilibrium that appears because of a highly directional patch attraction. Short attraction ranges preclude trimer formation, which explains why the protein system behaves as if it were subject to a concentration-dependent isotropic protein-protein attraction. Superimposing an isotropic interaction, comprising screened Coulomb repulsion and van der Waals attraction, on the patch attraction allows for a semiquantitative modeling of the complete transition pathway from monomers in the dilute limit to monomer-dimer systems at somewhat higher protein concentrations.
authors.forename: Weimin
authors.initials: W
authors.lastname: Li
authors.forename: Björn A
authors.initials: BA
authors.lastname: Persson
authors.forename: Mikael
authors.initials: M
authors.lastname: Lund
authors.affiliation: Department of Chemistry and Molecular Biology, University of Gothenburg , SE-412 96 Göteborg, Sweden.
authors.forename: Johan
authors.initials: J
authors.lastname: Bergenholtz
authors.forename: Malin
authors.initials: M
authors.lastname: Zackrisson Oskolkova
mesh_terms: D000818:Animals; D002417:Cattle; D007781:Lactoferrin / Q000032:analysis*; D053838:Scattering, Small Angle; D014961:X-Ray Diffraction
chemical_list: D007781:Lactoferrin