title: Ligand binding to distinct states diverts aggregation of an amyloid-forming protein.
abstract: Although small molecules that modulate amyloid formation in vitro have been identified, significant challenges remain in determining precisely how these species act. Here we describe the identification of rifamycin SV as a potent inhibitor of β(2) microglobulin (β(2)m) fibrillogenesis when added during the lag time of assembly or early during fibril elongation. Biochemical experiments demonstrate that the small molecule does not act by a colloidal mechanism. Exploiting the ability of electrospray ionization-ion mobility spectrometry-mass spectrometry (ESI-IMS-MS) to resolve intermediates of amyloid assembly, we show instead that rifamycin SV inhibits β(2)m fibrillation by binding distinct monomeric conformers, disfavoring oligomer formation and diverting the course of assembly to the formation of spherical aggregates. The results demonstrate the power of ESI-IMS-MS to identify specific protein conformers as targets for intervention in fibrillogenesis using small molecules and reveal a mechanism of action in which ligand binding diverts unfolded protein monomers toward alternative assembly pathways.
authors.affiliation: Astbury Centre for Structural Molecular Biology and Institute of Molecular and Cellular Biology, University of Leeds, Leeds, United Kingdom.
authors.forename: Lucy A
authors.initials: LA
authors.lastname: Woods
authors.forename: Geoffrey W
authors.initials: GW
authors.lastname: Platt
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Hellewell
authors.forename: Eric W
authors.initials: EW
authors.lastname: Hewitt
authors.forename: Steve W
authors.initials: SW
authors.lastname: Homans
authors.forename: Alison E
authors.initials: AE
authors.lastname: Ashcroft
authors.forename: Sheena E
authors.initials: SE
authors.lastname: Radford
mesh_terms: D001665:Binding Sites / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D011485:Protein Binding / Q000187:drug effects; D055503:Protein Multimerization / Q000187:drug effects*; D012294:Rifamycins / Q000737:chemistry / Q000494:pharmacology*; D021241:Spectrometry, Mass, Electrospray Ionization; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013997:Time Factors; D001613:beta 2-Microglobulin / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D008024:Ligands; D012294:Rifamycins; D001613:beta 2-Microglobulin; C023808:rifamycin SV