title: Toxicity of protein oligomers is rationalized by a function combining size and surface hydrophobicity.
abstract: The misfolding and aberrant assembly of peptides and proteins into fibrillar aggregates is the hallmark of many pathologies. Fibril formation is accompanied by oligomeric species thought to be the primary pathogenic agents in many of these diseases. With the aim of identifying the structural determinants responsible for the toxicity of misfolded oligomers, we created 12 oligomeric variants from the N-terminal domain of the E. coli HypF protein (HypF-N) by replacing one or more charged amino acid residues with neutral apolar residues and allowing the mutated proteins to aggregate under two sets of conditions. The resulting oligomeric species have different degrees of cytotoxicity when added to the extracellular medium of the cells, as assessed by the extent of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction, apoptosis, and influx of Ca2+ into the cells. The structural properties of the oligomeric variants were characterized by evaluating their surface hydrophobicity with 8-anilinonaphthalene-1-sulfonate (ANS) binding and by measuring their size by means of turbidimetry as well as light scattering. We find that increases in the surface hydrophobicity of the oligomers following mutation can promote the formation of larger assemblies and that the overall toxicity correlates with a combination of both surface hydrophobicity and size, with the most toxic oligomers having high hydrophobicity and small size. These results have allowed the relationships between these three parameters to be studied simultaneously and quantitatively, and have enabled the generation of an equation that is able to rationalize and even predict toxicity of the oligomers resulting from their surface hydrophobicity and size.
authors: Department of Biomedical Experimental and Clinical Sciences, Section of Biochemistry, University of Florence , 50134 Florence, Italy.
authors: Benedetta
authors: B
authors: Mannini
authors: Estefania
authors: E
authors: Mulvihill
authors: Caterina
authors: C
authors: Sgromo
authors: Roberta
authors: R
authors: Cascella
authors: Reza
authors: R
authors: Khodarahmi
authors: Matteo
authors: M
authors: Ramazzotti
authors: Christopher M
authors: CM
authors: Dobson
authors: Cristina
authors: C
authors: Cecchi
authors: Fabrizio
authors: F
authors: Chiti
mesh_terms: D019878:Carboxyl and Carbamoyl Transferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000633:toxicity; D049109:Cell Proliferation / Q000187:drug effects*; D002942:Circular Dichroism; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000633:toxicity; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions / Q000187:drug effects*; D009154:Mutation / Q000235:genetics; D055503:Protein Multimerization
chemical_list: D029968:Escherichia coli Proteins; D019878:Carboxyl and Carbamoyl Transferases; C504838:hypF protein, E coli