Regulation of the ribosome-membrane junction at early stages of presecretory protein translocation in the mammalian endoplasmic reticulum.

Journal Article

A series of fusion protein constructs were designed to investigate the contribution of secretory nascent chains to regulation of the ribosome-membrane junction in the mammalian endoplasmic reticulum. As a component of these studies, the membrane topology of the signal sequence was determined at stages of protein translocation immediately after targeting and before signal sequence cleavage. Truncated translation products were used to delimit the analysis to defined stages of translocation. In a study of secretory protein precursors, formation of a protease-resistant ribosome-membrane junction, currently thought to define the pathway of the translocating nascent chain, was observed to be precursor- and stage-dependent. Analysis of the binding of early intermediates indicated that the nascent chain was bound to the membrane independent of the ribosome, and that the binding was predominately electrostatic. The membrane topology of the signal sequence was determined as a function of the stage of translocation, and was found to be identical for all assayed intermediates. Unexpectedly, the hydrophobic core of the signal sequence was observed to be accessible to the cytosolic face of the membrane at stages of translocation immediately after targeting as well as stages before signal sequence cleavage. Removal of the ribosome from bound intermediates did not disrupt subsequent translocation, suggesting that the active state of the protein-conducting channel is maintained in the absence of the bound ribosome. A model describing a potential mode of regulation of the ribosome-membrane junction by the nascent chain is presented.

Full Text

Duke Authors

Cited Authors

  • Nicchitta, CV; Zheng, T

Published Date

  • December 29, 1997

Published In

Volume / Issue

  • 139 / 7

Start / End Page

  • 1697 - 1708

PubMed ID

  • 9412465

International Standard Serial Number (ISSN)

  • 0021-9525

Language

  • eng

Conference Location

  • United States