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Updated: Aug 9, 2026

Reconstitution of Msp1 Extraction Activity with Fully Purified Components
Published on: August 10, 2021
An ATP-binding membrane protein is required for protein translocation across the endoplasmic reticulum membrane
1Department of Biochemistry and Biophysics University of California, Medical School San Francisco 94143-0448.
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.
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