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Related Experiment Videos

Leaderless polypeptides efficiently extracted from whole cells by osmotic shock

Y R Thorstenson1, Y Zhang, P S Olson

  • 1Department of Molecular & Cell Biology, Celtrix Pharmaceuticals, Santa Clara, California 95054, USA.

Journal of Bacteriology
|September 1, 1997
PubMed
Summary

Leaderless bacterial and mammalian proteins accumulate in a specific E. coli compartment via a novel, signal sequence-independent mechanism. This conserved pathway suggests a broadly applicable intracellular localization system.

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Area of Science:

  • Molecular Biology
  • Cell Biology
  • Protein Localization

Background:

  • Protein translocation across cellular membranes typically relies on signal sequences.
  • The periplasmic compartment in Escherichia coli is a common destination for secreted proteins.
  • The mechanisms governing protein localization in the absence of signal sequences are not well understood.

Purpose of the Study:

  • To investigate the intracellular localization of bacterial (DsbA, DsbC, rotamase) and mammalian (IL-1 receptor antagonist) proteins lacking their native signal sequences in E. coli.
  • To identify the mechanism responsible for the localization of these leaderless proteins.
  • To determine if this localization mechanism is conserved across species.

Main Methods:

  • Site-directed mutagenesis to remove signal sequences from target proteins.

Related Experiment Videos

  • Overexpression of leaderless proteins in E. coli.
  • Cell fractionation and extraction techniques to isolate proteins.
  • Biochemical assays (e.g., beta-galactosidase complementation) and genetic analysis (secA, ftsZ dependence).

    • Main Results:

    • Leaderless DsbA, DsbC, rotamase, and IL-1 receptor antagonist accumulated in an osmotically sensitive cellular compartment.
    • These leaderless proteins were extractable using methods for periplasmic proteins but were not associated with membranes.
    • Localization was independent of the secA and ftsZ transport pathways, indicating a novel mechanism.

    Conclusions:

    • A signal sequence-independent mechanism facilitates the translocation of specific leaderless proteins to a unique cellular compartment in E. coli.
    • Structurally unrelated proteins, including a mammalian protein, are recognized by this bacterial localization system.
    • The findings suggest a conserved, evolutionarily broad mechanism for intracellular protein targeting.