Subunit dynamics in Escherichia coli preprotein translocase

Area of Science:

• Molecular Biology
• Cell Biology
• Microbiology

Background:

• The SecY/E complex is the core of the preprotein translocase in Escherichia coli, a vital system for protein secretion across the inner membrane.
• Understanding the assembly dynamics and subunit exchange of the SecY/E complex is crucial for elucidating protein translocation mechanisms.

Purpose of the Study:

• To investigate the in vivo association stability of SecY and SecE subunits within the Escherichia coli preprotein translocase.
• To determine if SecY and SecE subunits can exchange within the functional SecY/E complex in living cells.

Main Methods:

• Utilized plasmid-borne secY and secE genes under arabinose regulon control in Escherichia coli.
• Introduced influenza hemagglutinin epitope tags to secY and secE genes for detection.
• Employed [35S]methionine labeling followed by a chase period and arabinose induction for pulse-chase experiments.
• Performed immunoprecipitation using antibodies against the epitope tag to assess subunit association.

Main Results:

• Both wild-type and epitope-tagged SecY and SecE polypeptides successfully assembled into functional, heterotrimeric SecY/E complexes.
• Immunoprecipitation of epitope-tagged SecY or SecE did not result in the co-precipitation of radiolabeled SecY or SecE subunits.
• This indicates a lack of exchange between newly synthesized and existing subunits within the complex.

Conclusions:

• SecY and SecE subunits associate stably in vivo, forming a non-exchangeable heterotrimeric complex.
• The findings suggest a highly stable assembly mechanism for the SecY/E translocase, critical for its function in protein translocation.