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SecA supports a constant rate of preprotein translocation

Danuta Tomkiewicz1, Nico Nouwen, Ruud van Leeuwen

  • 1Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute and the Materials Science Centre Plus, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands.

The Journal of Biological Chemistry
|April 8, 2006
PubMed

Insights

The SecA motor protein drives preprotein translocation across bacterial membranes. Longer protein chains increase translocation delay but not the rate, supporting a stepwise SecA mechanism.

Area of Science:

  • Molecular Biology
  • Cellular Biology
  • Biochemistry

Background:

  • The Sec system in Escherichia coli facilitates protein translocation across the cytoplasmic membrane.
  • This system involves the SecYEG channel and the ATP-dependent motor protein SecA.
  • SecA is believed to drive protein translocation through cycles of ATP binding and hydrolysis.

Purpose of the Study:

  • To investigate the impact of preprotein substrate length on SecA-driven translocation.
  • To determine if SecA maintains a constant translocation rate regardless of substrate size.

Main Methods:

  • Constructed proOmpA derivatives with varying lengths of tandem repeats.
  • Analyzed translocation times and rates using these modified substrates.
  • Studied the SecA-driven translocation process in Escherichia coli.

Main Results:

  • Increasing polypeptide length of proOmpA derivatives resulted in a longer delay before complete translocation.
  • The translocation rate, measured in amino acids per minute, remained constant across different lengths.
  • This suggests SecA operates with a consistent speed per translocation step.

Conclusions:

  • SecA-driven protein translocation is a stepwise process.
  • The length of the preprotein substrate influences the overall translocation time due to sequential steps, not a change in motor speed.
  • This provides evidence for a constant-rate stepping mechanism of SecA in protein translocation.

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