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Lack of coupling between secondary structure formation and collapse in a model polypeptide that mimics early folding intermediates, the F 2 fragment of the Escherichia coli tryptophan‐synthase β chain
Author(s) -
Gast Klaus,
MuellerFrohne Marlies,
Chaffotte Alain F.,
Guillou Yvonne,
Hodges Maria,
Cadieux CÉLine,
Goldberg Michel E.,
Zirwer Dietrich,
Damaschun Gregor
Publication year - 1997
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1002/pro.5560061210
Subject(s) - protein secondary structure , chemistry , tryptophan synthase , folding (dsp implementation) , protein folding , crystallography , stokes radius , hofmeister series , protein tertiary structure , protein structure , folding funnel , protein primary structure , contact order , tryptophan , phi value analysis , enzyme , downhill folding , amino acid , peptide sequence , biochemistry , ion , organic chemistry , size exclusion chromatography , electrical engineering , gene , engineering
The isolated, 101‐residue long C‐terminal (so called F 2 ) fragment of the β 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 F 2 . 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 F 2 , 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 F 2 . Conversely, F 2 became more condensed upon raising the temperature from 4 to 60°C, whereas in this temperature range, the secondary structure undergoes significant melting. These observations lead to the conclusion that, in isolated F 2 , 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.