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Bacteria have global regulatory systems that control several types of stress mechanisms. These include Pho regulon and the heat shock response, which are essential systems for environmental adaptation, such as nutrient limitation and proteotoxic stress. The Pho regulon and the heat shock response exemplify bacterial resilience, enabling rapid adaptation to fluctuating environmental conditions.Pho RegulonBacteria require phosphorus for essential cellular processes, including nucleic acid...
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Related Experiment Video

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Intracellular Refolding Assay
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Crowding Activates Heat Shock Protein 90.

Jackson C Halpin1, Bin Huang1, Ming Sun1

  • 1From the Department of Biochemistry, Brandeis University, Waltham, Massachusetts 02454.

The Journal of Biological Chemistry
|January 23, 2016
PubMed
Summary

Molecular crowding significantly enhances the ATPase activity of heat shock protein 90 (Hsp90) by favoring its closed state. This effect, driven by entropy, suggests Hsp90 functions more actively within cells than previously thought.

Keywords:
ATPasechaperoneconformational changeheat shock protein 90 (Hsp90)macromolecular crowding

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Cellular Biophysics

Background:

  • Heat shock protein 90 (Hsp90) is a crucial ATP-dependent chaperone regulating protein homeostasis.
  • Current models of Hsp90 function are based on dilute in vitro conditions, potentially overlooking cellular complexities.

Purpose of the Study:

  • To investigate the impact of molecular crowding on Hsp90's ATPase activity and conformational dynamics.
  • To compare Hsp90's response to crowding with other chaperones like Hsp60 and Hsp70.

Main Methods:

  • Utilized polymer crowders to simulate cellular environments and measured Hsp90 ATPase activity.
  • Performed structural and thermodynamic analyses to understand crowding effects.
  • Assessed the sensitivity of Hsp90 homologs, including Grp94, to crowding.

Main Results:

  • Hsp90 ATPase activity is highly sensitive to molecular crowding, unlike Hsp60 and Hsp70.
  • Crowding activates Hsp90 in a non-saturable, concentration-dependent manner, favoring the closed conformation entropically.
  • Endoplasmic reticulum-specific Hsp90 (Grp94) showed the highest sensitivity to crowding.

Conclusions:

  • Molecular crowding significantly influences Hsp90 function, suggesting higher intrinsic activity in vivo.
  • Crowding activation is mechanistically distinct and independent of co-chaperone activation.
  • The findings challenge the applicability of dilute solution models for Hsp90 in cellular contexts.