The folding pathway of T4 lysozyme: an on-pathway hidden folding intermediate

J Mol Biol. 2007 Jan 19;365(3):881-91. doi: 10.1016/j.jmb.2006.10.048. Epub 2006 Oct 21.

Abstract

T4 lysozyme has two easily distinguishable but energetically coupled domains: the N and C-terminal domains. In earlier studies, an amide hydrogen/deuterium exchange pulse-labeling experiment detected a stable submillisecond intermediate that accumulates before the rate-limiting transition state. It involves the formation of structures in both the N and C-terminal regions. However, a native-state hydrogen exchange experiment subsequently detected an equilibrium intermediate that only involves the formation of the C-terminal domain. Here, using stopped-flow circular dichroism and fluorescence, amide hydrogen exchange-folding competition, and protein engineering methods, we re-examined the folding pathway of T4-lysozyme. We found no evidence for the existence of a stable folding intermediate before the rate-limiting transition state at neutral pH. In addition, using native-state hydrogen exchange-directed protein engineering, we created a mimic of the equilibrium intermediate. We found that the intermediate mimic folds with the same rate as the wild-type protein, suggesting that the equilibrium intermediate is an on-pathway intermediate that exists after the rate-limiting transition state.

Publication types

  • Research Support, N.I.H., Intramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacteriophage T4 / enzymology*
  • Circular Dichroism
  • Fluorescence
  • Hydrogen
  • Hydrogen-Ion Concentration
  • Kinetics
  • Muramidase / chemistry*
  • Muramidase / metabolism*
  • Mutant Proteins / chemistry
  • Mutant Proteins / metabolism
  • Protein Engineering
  • Protein Folding*
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Temperature
  • Time Factors

Substances

  • Mutant Proteins
  • Hydrogen
  • Muramidase