title: Lack of coupling between secondary structure formation and collapse in a model polypeptide that mimics early folding intermediates, the F2 fragment of the Escherichia coli tryptophan-synthase beta chain.
abstract: The isolated, 101-residue long C-terminal (so called F2) fragment of the beta chain from Escherichia coli tryptophan synthase was shown previously to fold into an ensemble of conformations that are condensed, to contain large amounts of highly dynamic secondary structures, and to behave as a good model of structured intermediates that form at the very early stages of protein folding. Here, solvent perturbations were used to investigate the forces that are involved in stabilizing the secondary structure (monitored by far-UV CD) and the condensation of the polypeptide chain (monitored by dynamic light scattering) in isolated F2. It was observed that neither the ionic strength, nor the pH (between 7 and 10), nor salts of the Hofmeister series affected the global secondary structure contents of F2, whereas some of these salts affected the collapse slightly. Addition of trifluoroethanol resulted in a large increase in both the amount of secondary structure and the Stokes radius of F2. Conversely, F2 became more condensed upon raising the temperature from 4 to 60 degrees C, whereas in this temperature range, the secondary structure undergoes significant melting. These observations lead to the conclusion that, in isolated F2, there is no coupling between the hydrophobic collapse and the secondary structure. This finding will be discussed in terms of early events in protein folding.
authors.affiliation: Max Delbrück Center for Molecular Medicine, Berlin, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Gast
authors.forename: A F
authors.initials: AF
authors.lastname: Chaffotte
authors.forename: D
authors.initials: D
authors.lastname: Zirwer
authors.forename: Y
authors.initials: Y
authors.lastname: Guillou
authors.forename: M
authors.initials: M
authors.lastname: Mueller-Frohne
authors.forename: C
authors.initials: C
authors.lastname: Cadieux
authors.forename: M
authors.initials: M
authors.lastname: Hodges
authors.forename: G
authors.initials: G
authors.lastname: Damaschun
authors.forename: M E
authors.initials: ME
authors.lastname: Goldberg
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002942:Circular Dichroism; D019281:Dimerization; D004795:Enzyme Stability / Q000187:drug effects; D004926:Escherichia coli / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D008970:Molecular Weight; D009994:Osmolar Concentration; D010446:Peptide Fragments / Q000737:chemistry*; D010710:Phosphates / Q000494:pharmacology; D019347:Potassium Acetate / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D017680:Potassium Compounds / Q000494:pharmacology; D017510:Protein Folding; D017433:Protein Structure, Secondary; D014270:Trifluoroethanol / Q000494:pharmacology; D014367:Tryptophan Synthase / Q000737:chemistry*
chemical_list: D010446:Peptide Fragments; D010710:Phosphates; D017680:Potassium Compounds; D011189:Potassium Chloride; D014270:Trifluoroethanol; C013216:potassium phosphate; D014367:Tryptophan Synthase; D019347:Potassium Acetate