Inhibition of protein translocation across the endoplasmic reticulum membrane by sterols.

Ingmarie Nilsson,J Peter Slotte,Henna Ohvo-Rekilä,Gunnar Von Heijne,Arthur E Johnson

doi:10.1074/jbc.m105823200

Abstract

Cholesterol and related sterols are known to modulate the physical properties of biological membranes and can affect the activities of membrane-bound protein complexes. Here, we report that an early step in protein translocation across the endoplasmic reticulum (ER) membrane is reversibly inhibited by cholesterol levels significantly lower than those found in the plasma membrane. By UV-induced chemical cross-linking we further show that high cholesterol levels prevent cross-linking between ribosome-nascent chain complexes and components of the Sec61 translocon, but have no effect on cross-linking to the signal recognition particle. The inhibiting effect on translocation is different between different sterols. Our data suggest that the protein translocation machinery may be sensitive to changes in cholesterol levels in the ER membrane.

Highlights

Sterols are known to modulate the physical properties of biological membranes [1,2,3,4]
We report that an early step in protein translocation across the endoplasmic reticulum (ER) membrane is reversibly inhibited by cholesterol levels significantly lower than those found in the plasma membrane
We report that an early step in protein translocation across the ER membrane is reversibly inhibited by cholesterol levels significantly lower than those found in the plasma membrane

Summary

Introduction

Sterols are known to modulate the physical properties of biological membranes [1,2,3,4]. We report that an early step in protein translocation across the ER membrane is reversibly inhibited by cholesterol levels significantly lower than those found in the plasma membrane. By UV-induced chemical cross-linking we further show that high cholesterol levels prevent cross-linking between ribosome-nascent chain complexes (RNCs) and components of the Sec translocon, but have no effect on crosslinking of RNCs to the signal recognition particle (SRP). These observations suggest that an increase in membrane stiffness renders the Sec protein translocation machinery in the ER unable to recognize and/or initiate translocation of nascent polypeptide chains. One possible implication of our findings is that Sec translocons that have leaked out to the Golgi compartment and beyond [23] may be rendered nonfunctional by cholesterol-mediated inhibition

Methods

Results

Conclusion