BiP acts as a molecular ratchet during posttranslational transport of prepro-alpha factor across the ER membrane

Cell. 1999 May 28;97(5):553-64. doi: 10.1016/s0092-8674(00)80767-9.

Abstract

We have addressed the mechanism by which proteins are posttranslationally transported across the membrane of the yeast endoplasmic reticulum (ER). We demonstrate that BiP (Kar2p), a member of the Hsp70 family resident in the ER lumen, acts as a molecular ratchet during translocation of the secretory protein prepro-alpha factor through the channel formed by the Sec complex. Multiple BiP molecules associate with each translocation substrate following interaction with the J domain of the Sec63p component of the Sec complex. Bound BiP minimizes passive backward movements of the substrate through the channel, and BiP's subsequent dissociation results in a free polypeptide in the ER lumen. Antibodies against the substrate can replace BiP, indicating that a Brownian ratchet is sufficient to achieve translocation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Cloning, Molecular
  • Endoplasmic Reticulum / metabolism*
  • Escherichia coli
  • Fungal Proteins / chemistry
  • Fungal Proteins / metabolism*
  • HSP70 Heat-Shock Proteins / chemistry
  • HSP70 Heat-Shock Proteins / metabolism*
  • Intracellular Membranes / metabolism
  • Kinetics
  • Mating Factor
  • Molecular Sequence Data
  • Peptides / genetics
  • Protein Binding
  • Protein Biosynthesis
  • Protein Precursors / metabolism*
  • Protein Processing, Post-Translational*
  • Recombinant Proteins / metabolism
  • Saccharomyces cerevisiae / metabolism*
  • Saccharomyces cerevisiae Proteins*

Substances

  • Fungal Proteins
  • HSP70 Heat-Shock Proteins
  • KAR2 protein, yeast
  • MF(ALPHA)1 protein, S cerevisiae
  • Peptides
  • Protein Precursors
  • Recombinant Proteins
  • Saccharomyces cerevisiae Proteins
  • Mating Factor