Studying the folding process of the acylphosphatase from Sulfolobus solfataricus. A comparative analysis with other proteins from the same superfamily

Year: 2004

Authors: Bemporad F., Capanni C., Calamai M., Tutino ML., Stefani M., Chiti F.

Autors Affiliation: Dipartimento di Scienze Biochimiche, Universita` di Firenze, Viale Morgagni 50, 50134 Firenze, Italy;
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, U.K.;
Dipartimento di Chimica Organica e Biochimica, Universita` di Napoli, Edificio MB, Via Cinthia, Monte S. Angelo, 80100 Napoli, Italy

Abstract: The folding process of the acylphosphatase from Sulfolobus solfataricus (Sso AcP) has been followed, starting from the fully unfolded state, using a variety of spectroscopic probes, including intrinsic fluorescence, circular dichroism, and ANS binding. The results indicate that an ensemble of partially folded or misfolded species form rapidly on the submillisecond time scale after initiation of folding. This conformational ensemble produces a pronounced downward curvature in the Chevron plot, appears to possess a content of secondary structure similar to that of the native state, as revealed by far-UV circular dichroism, and appears to have surface-exposed hydrophobic clusters, as indicated by the ability of this ensemble to bind to 8-anilino-1-naphthalenesulfonic acid (ANS). Sso AcP folds from this conformational state with a rate constant of ca. 5 s(-1) at pH 5.5 and 37 degreesC. A minor slow exponential phase detected during folding (rate constant of 0.2 s(-1) under these conditions) is accelerated by cyclophilin A and is absent in a mutant of Sso AcP in which alanine replaces the proline residue at position 50. This indicates that for a lower fraction of Sso AcP molecules the folding process is rate-limited by the cis-trans isomerism of the peptide bond preceding Pro50. A comparative analysis with four other homologous proteins from the acylphosphatase superfamily shows that sequence hydrophobicity is an important determinant of the conformational stability of partially folded states that may accumulate during folding of a protein. A low net charge and a high propensity to form alpha-helical structure also emerge as possibly important determinants of the stability of partially folded states. A significant correlation is also observed between folding rate and hydrophobic content of the sequence within this superfamily, lending support to the idea that sequence hydrophobicity, in addition to relative contact order and conformational stability of the native state, is a key determinant of folding rate.

Journal/Review: BIOCHEMISTRY

Volume: 43(28)      Pages from: 9116  to: 9126

KeyWords: Chemical bonds; Hydrophobicity; Organic acids; Proteins; Spectroscopic analysis, Intrinsic fluorescence; Secondary structures, Biochemistry, 8 anilino 1 naphthalenesulfonic acid; acylphosphatase; alanine; cyclophilin A; peptide; proline, alpha helix; amino acid substitution; article; chemical bond; circular dichroism; cis trans isomerism; enzyme binding; enzyme conformation; enzyme stability; fluorescence; hydrophobicity; nonhuman; pH; priority journal; protein folding; protein secondary structure; reaction time; Sulfolobus solfataricus, Acid Anhydride Hydrolases; Amino Acid Sequence; Amino Acid Substitution; Cyclophilin A; Hydrophobicity; Kinetics; Protein Folding; Protein Structure, Secondary; Spectrum Analysis; Sulfolobus, Sulfolobus; Sulfolobus solfataricus
DOI: 10.1021/bi030238a

Citations: 18
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