title: An ATP-binding membrane protein is required for protein translocation across the endoplasmic reticulum membrane.
abstract: The role of nucleotides in providing energy for polypeptide transfer across the endoplasmic reticulum (ER) membrane is still unknown. To address this question, we treated ER-derived mammalian microsomal vesicles with a photoactivatable analogue of ATP, 8-N3ATP. This treatment resulted in a progressive inhibition of translocation activity. Approximately 20 microsomal membrane proteins were labeled by [alpha 32P]8-N3ATP. Two of these were identified as proteins with putative roles in translocation, alpha signal sequence receptor (SSR), the 35-kDa subunit of the signal sequence receptor complex, and ER-p180, a putative ribosome receptor. We found that there was a positive correlation between inactivation of translocation activity and photolabeling of alpha SSR. In contrast, our data demonstrate that the ATP-binding domain of ER-p180 is dispensable for translocation activity and does not contribute to the observed 8-N3ATP sensitivity of the microsomal vesicles.
authors.affiliation: Department of Biochemistry and Biophysics University of California, Medical School San Francisco 94143-0448.
authors.forename: D L
authors.initials: DL
authors.lastname: Zimmerman
authors.forename: P
authors.initials: P
authors.lastname: Walter
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism*; D000345:Affinity Labels; D000818:Animals; D001386:Azides; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D008861:Microsomes / Q000378:metabolism; D021382:Protein Sorting Signals / Q000378:metabolism
chemical_list: D000345:Affinity Labels; D001386:Azides; D002352:Carrier Proteins; D008565:Membrane Proteins; D021382:Protein Sorting Signals; C017040:8-azidoadenosine 5'-triphosphate; D000255:Adenosine Triphosphate