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Microfluidic Mixers for Studying Protein Folding
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Published on: April 10, 2012

Microsecond folding dynamics of apomyoglobin at acidic pH.

Ming Xu1, Olga Beresneva, Ryan Rosario

  • 1Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.

The Journal of Physical Chemistry. B
|April 6, 2012
PubMed
Summary

This study reveals rapid intermediate states during apomyoglobin folding at pH 4.2, providing new insights into helical protein folding mechanisms and conformational barriers.

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Area of Science:

  • Protein folding mechanisms
  • Biophysical chemistry
  • Structural biology

Background:

  • Apomyoglobin (apoMb) serves as a key model for studying helical protein folding.
  • A partially structured state (M-state) at pH 4.2 resembles a late kinetic intermediate in apoMb folding.
  • Understanding intermediate states is crucial for elucidating protein folding pathways.

Purpose of the Study:

  • To investigate the thermodynamics and kinetics of apoMb folding at pH 4.2 and 6.2.
  • To characterize the previously unresolved intermediate states in apoMb folding and unfolding.
  • To gain insight into the conformational states and energy barriers preceding the rate-limiting step in native state formation.

Main Methods:

  • Global analysis of urea-induced unfolding transitions monitored by tryptophan fluorescence and circular dichroism.
  • Time-resolved fluorescence-detected continuous-flow measurements for kinetic studies.
  • Quantitative kinetic modeling using a four-state mechanism (U↔I↔L↔M).

Main Results:

  • Biphasic kinetics observed in apoMb folding and unfolding at pH 4.2.
  • Rapid (<100 μs) accumulation of intermediate states identified.
  • Thermodynamic and kinetic parameters for folding at pH 4.2 and 6.2 were determined.
  • A four-state kinetic model elucidated the pathway involving two intermediates.

Conclusions:

  • The study provides evidence for rapid formation of intermediate states in apoMb folding.
  • New insights into the conformational landscape and kinetic barriers of apoMb folding were obtained.
  • The findings contribute to a deeper understanding of helical protein folding mechanisms.