title: Structural characterization of microcin E492 amyloid formation: Identification of the precursors.
abstract: Microcin E492 is a low-molecular weight, channel-forming bacteriotoxin that generates amyloid structures. Using electron microscopy and image processing techniques several structural conformations can be observed. Prior to the conditions that induce amyloid formation and at its initial stage, microcin E492 molecules can be found in two main types of oligomers: a pentameric, pore-like structure consisting of globular monomers of ∼25Å diameter, and long filaments made up of stacked pentamers. The equilibrium between these structures depends on the properties of the solvent, because samples kept in methanol mainly show the pentameric structure. Amyloid induction in aqueous solvent reveals the presence, together with the above mentioned structures, of several amyloid structures such as flat and helical filaments. In addition, X-ray diffraction analysis demonstrated that the fibrils formed by microcin E492 presented cross-β structure, a distinctive property of amyloid fibrils. Based on the study of the observed structures we propose that microcin E492 has two conformations: a native one that assembles mainly into a pentameric structure, which functions as a pore, and an amyloid conformation which results in the formation of different types of amyloid filaments.
authors.affiliation: Centro Nacional de Biotecnología (CNB-CSIC), Campus de Cantoblanco, Madrid, Spain.
authors.forename: Rocío
authors.initials: R
authors.lastname: Arranz
authors.forename: Gabriela
authors.initials: G
authors.lastname: Mercado
authors.forename: Jaime
authors.initials: J
authors.lastname: Martín-Benito
authors.forename: Rafael
authors.initials: R
authors.lastname: Giraldo
authors.forename: Octavio
authors.initials: O
authors.lastname: Monasterio
authors.forename: Rosalba
authors.initials: R
authors.lastname: Lagos
authors.forename: José M
authors.initials: JM
authors.lastname: Valpuesta
mesh_terms: D000682:Amyloid / Q000096:biosynthesis / Q000737:chemistry / Q000648:ultrastructure; D001430:Bacteriocins / Q000737:chemistry*; D007711:Klebsiella pneumoniae / Q000378:metabolism / Q000472:pathogenicity; D008854:Microscopy, Electron; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D014961:X-Ray Diffraction
chemical_list: D000682:Amyloid; D001430:Bacteriocins; C020411:microcin