Relative influence of hydrophobicity and net charge in the aggregation of two homologous proteins

Year: 2003

Authors: Calamai M., Taddei N., Stefani M., Ramponi G., Chiti F.

Autors Affiliation: Dipartimento di Scienze Biochimiche, Universita` degli Studi di Firenze, Viale Morgagni 50, 50134 Firenze, Italy

Abstract: A potentially amyloidogenic protein has to be at least partially unfolded to form amyloid aggregates. However, aggregation of the partially or totally unfolded state of a protein is modulated by at least three other factors: hydrophobicity, propensity to form secondary structure, and net charge of the polypeptide chain. We propose to evaluate the relative importance of net charge, as opposed to the other factors, on protein aggregation and amyloidogenicity. For this aim, we have used two homologous proteins that were previously shown to be able to form amyloid fibrils in vitro, the N-terminal domain of HypF from Escherichia coli (HypF-N) and human muscle acylphosphatase (AcP). The aggregation process from an ensemble of partially unfolded conformations is ca. 1000-fold faster for HypF-N than for AcP. This difference can mainly be attributed to a higher hydrophobicity and a lower net charge for HypF-N than for AcP. By using protein engineering methods, we have decreased the net charge of AcP to a value identical to that of wild-type HypF-N and increased the net charge of HypF-N to a value identical to that of wild-type AcP. Amino acid substitutions were selected to minimize changes in hydrophobicity and secondary structure propensities. We were able to estimate that the difference in net charge between the two wild-type proteins contributes to 20-25% of the difference in their aggregation rates. An understanding of the relative influences of these forces in protein aggregation has implications for elucidating the complexity of the aggregation process, for predicting the effect of natural mutations, and for accurate protein design.

Journal/Review: BIOCHEMISTRY

Volume: 42(51)      Pages from: 15078  to: 15083

KeyWords: Agglomeration; Amino acids; Escherichia coli; Hydrophobicity, Mutations, Proteins, acylphosphatase; amyloid, alpha helix; amino acid substitution; amino terminal sequence; article; Escherichia coli; hydrophobicity; priority journal; protein aggregation; protein engineering; protein folding; protein secondary structure, Acid Anhydride Hydrolases; Amino Acid Substitution; Bacterial Proteins; Electrostatics; Escherichia coli Proteins; Humans; Hydrophobicity; Kinetics; Muscle Proteins; Mutagenesis, Site-Directed; Peptide Fragments; Protein Denaturation; Sequence Homology, Amino Acid, Escherichia coli
DOI: 10.1021/bi030135s

Citations: 104
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