title: Amyloid fibril formation by an SH3 domain.
abstract: The SH3 domain is a well characterized small protein module with a simple fold found in many proteins. At acid pH, the SH3 domain (PI3-SH3) of the p85alpha subunit of bovine phosphatidylinositol 3-kinase slowly forms a gel that consists of typical amyloid fibrils as assessed by electron microscopy, a Congo red binding assay, and x-ray fiber diffraction. The soluble form of PI3-SH3 at acid pH (the A state by a variety of techniques) from which fibrils are generated has been characterized. Circular dichroism in the far- and near-UV regions and 1H NMR indicate that the A state is substantially unfolded relative to the native protein at neutral pH. NMR diffusion measurements indicate, however, that the effective hydrodynamic radius of the A state is only 23% higher than that of the native protein and is 20% lower than that of the protein denatured in 3.5 M guanidinium chloride. In addition, the A state binds the hydrophobic dye 1-anilinonaphthalene-8-sulfonic acid, which suggests that SH3 in this state has a partially formed hydrophobic core. These results indicate that the A state is partially folded and support the hypothesis that partially folded states formed in solution are precursors of amyloid deposition. Moreover, that this domain aggregates into amyloid fibrils suggests that the potential for amyloid deposition may be a common property of proteins, and not only of a few proteins associated with disease.
authors.affiliation: Oxford Centre for Molecular Sciences, University of Oxford, South Parks Road, Oxford OX1 3QT, United Kingdom.
authors.forename: J I
authors.initials: JI
authors.lastname: Guijarro
authors.forename: M
authors.initials: M
authors.lastname: Sunde
authors.forename: J A
authors.initials: JA
authors.lastname: Jones
authors.forename: I D
authors.initials: ID
authors.lastname: Campbell
authors.forename: C M
authors.initials: CM
authors.lastname: Dobson
mesh_terms: D000682:Amyloid / Q000737:chemistry* / Q000648:ultrastructure*; D000817:Anilino Naphthalenesulfonates; D000818:Animals; D002417:Cattle; D002942:Circular Dichroism; D005456:Fluorescent Dyes; D006801:Humans; D008854:Microscopy, Electron; D019906:Nuclear Magnetic Resonance, Biomolecular; D019869:Phosphatidylinositol 3-Kinases / Q000737:chemistry / Q000648:ultrastructure; D011487:Protein Conformation; D017510:Protein Folding; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000648:ultrastructure; D014961:X-Ray Diffraction; D018909:src Homology Domains
chemical_list: D000682:Amyloid; D000817:Anilino Naphthalenesulfonates; D005456:Fluorescent Dyes; D011993:Recombinant Fusion Proteins; C027132:1-anilino-8-naphthalenesulfonate; D019869:Phosphatidylinositol 3-Kinases