SecA supports a constant rate of preprotein translocation

J Biol Chem. 2006 Jun 9;281(23):15709-13. doi: 10.1074/jbc.M600205200. Epub 2006 Apr 6.

Abstract

In Escherichia coli, secretory proteins (preproteins) are translocated across the cytoplasmic membrane by the Sec system composed of a protein-conducting channel, SecYEG, and an ATP-dependent motor protein, SecA. After binding of the preprotein to SecYEG-bound SecA, cycles of ATP binding and hydrolysis by SecA are thought to drive the stepwise translocation of the preprotein across the membrane. To address how the length of a preprotein substrate affects the SecA-driven translocation process, we constructed derivatives of the precursor of the outer membrane protein A (proOmpA) with 2, 4, 6, and 8 in-tandem repeats of the periplasmic domain. With increasing polypeptide length, an increasing delay in the time before full-length translocation was observed, but the translocation rate expressed as amino acid translocation per minute remained constant. These data indicate that in the ATP-dependent reaction, SecA drives a constant rate of preprotein translocation consistent with a stepping mechanism of translocation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphatases / physiology*
  • Adenosine Triphosphate / metabolism
  • Bacterial Proteins / physiology*
  • Hydrolysis
  • Kinetics
  • Membrane Transport Proteins / physiology*
  • Protein Precursors / metabolism
  • Protein Transport
  • SEC Translocation Channels
  • SecA Proteins

Substances

  • Bacterial Proteins
  • Membrane Transport Proteins
  • Protein Precursors
  • SEC Translocation Channels
  • Adenosine Triphosphate
  • Adenosine Triphosphatases
  • SecA Proteins