Intrinsically disordered and aggregation prone regions underlie β-aggregation in S100 proteins

• Published in: PloS one Vol. 8; no. 10; p. e76629
• Main Authors: Carvalho, Sofia B, Botelho, Hugo M, Leal, Sónia S, Cardoso, Isabel, Fritz, Günter, Gomes, Cláudio M
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 01-10-2013; Public Library of Science (PLoS)
• Subjects: Agglomeration; Amino Acid Sequence; Amyotrophic lateral sclerosis; Antibodies; Binding; Biodiversity; Calcium; Cell cycle; Computer Simulation; Dominant species; Fibrils; Flocculation; Fluorescence; Helices; Humans; Hydrogen-Ion Concentration; Hydrophobic and Hydrophilic Interactions; Hydrophobicity; Lag phase; Metastasis; Models, Molecular; Molecular Sequence Data; Neurosciences; Peptide Mapping; Prostate; Protein Folding; Protein Stability; Protein structure; Protein Structure, Quaternary; Protein Structure, Secondary; Protein Structure, Tertiary; Proteins; Quaternary structure; Recombinant Proteins - chemistry; Recombinant Proteins - genetics; S100 Proteins - chemistry; S100 Proteins - genetics; Seeds; Segments; Sequence Alignment; Sequence Homology, Amino Acid; Shielding; Species diversity; Spectrum analysis; Superoxide dismutase; Portugal
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0076629

S100 proteins are small dimeric calcium-binding proteins which control cell cycle, growth and differentiation via interactions with different target proteins. Intrinsic disorder is a hallmark among many signaling proteins and S100 proteins have been proposed to contain disorder-prone regions. Interestingly, some S100 proteins also form amyloids: S100A8/A9 forms fibrils in prostatic inclusions and S100A6 fibrillates in vitro and seeds SOD1 aggregation. Here we report a study designed to investigate whether β-aggregation is a feature extensive to more members of S100 family. In silico analysis of seven human S100 proteins revealed a direct correlation between aggregation and intrinsic disorder propensity scores, suggesting a relationship between these two independent properties. Averaged position-specific analysis and structural mapping showed that disorder-prone segments are contiguous to aggregation-prone regions and that whereas disorder is prominent on the hinge and target protein-interaction regions, segments with high aggregation propensity are found in ordered regions within the dimer interface. Acidic conditions likely destabilize the seven S100 studied by decreasing the shielding of aggregation-prone regions afforded by the quaternary structure. In agreement with the in silico analysis, hydrophobic moieties become accessible as indicated by strong ANS fluorescence. ATR-FTIR spectra support a structural inter-conversion from α-helices to intermolecular β-sheets, and prompt ThT-binding takes place with no noticeable lag phase. Dot blot analysis using amyloid conformational antibodies denotes a high diversity of conformers; subsequent analysis by TEM shows fibrils as dominant species. Altogether, our data suggests that β-aggregation and disorder-propensity are related properties in S100 proteins, and that the onset of aggregation is likely triggered by loss of protective tertiary and quaternary interactions.