Motor recruitment to the TIM23 channel\u2019s lateral gate restricts polypeptide release into the inner membrane

Alexander Benjamin Schendzielorz,Peter Rehling,Agnieszka Chacinska,Ridhima Gomkale,Nataliia Naumenko,Bernard Guiard,Piotr Bragoszewski,Christian Schulz

doi:10.1038/s41467-018-06492-8

Abstract

The presequence translocase of the mitochondrial inner membrane (TIM23 complex) facilitates anterograde precursor transport into the matrix and lateral release of precursors with stop-transfer signal into the membrane (sorting). Sorting requires precursor exit from the translocation channel into the lipid phase through the lateral gate of the TIM23 complex. How the two transport modes are regulated and balanced against each other is unknown. Here we show that the import motor J-protein Pam18, which is essential for matrix import, controls lateral protein release into the lipid bilayer. Constitutively translocase-associated Pam18 obstructs lateral precursor transport. Concomitantly, Mgr2, implicated in precursor quality control, is displaced from the translocase. We conclude that during motor-dependent matrix protein transport, the transmembrane segment of Pam18 closes the lateral gate to promote anterograde polypeptide movement. This finding explains why a motor-free form of the translocase facilitates the lateral movement of precursors with a stop-transfer signal.

Highlights

The presequence translocase of the mitochondrial inner membrane (TIM23 complex) facilitates anterograde precursor transport into the matrix and lateral release of precursors with stop-transfer signal into the membrane
The TIM23 complex facilitates the transport of two basic types of precursors (i) matrix proteins that are fully translocated across the inner membrane and depend on the activity of the ATP-driven import motor for transport; (ii) inner membrane proteins that are stalled during the process of inner membrane translocation and laterally released into the lipid phase[5,6,8,9,10]
Since the intermembrane space exposed C-terminal domain of Tim[17] transiently interacts with the N-terminal domain of Pam[18], we reasoned that this fusion protein would closely resemble the physiological translocaseassociated state (Fig. 1a)

Summary

Introduction

The presequence translocase of the mitochondrial inner membrane (TIM23 complex) facilitates anterograde precursor transport into the matrix and lateral release of precursors with stop-transfer signal into the membrane (sorting). The TIM23 complex facilitates the transport of two basic types of precursors (i) matrix proteins that are fully translocated across the inner membrane and depend on the activity of the ATP-driven import motor for transport; (ii) inner membrane proteins that are stalled during the process of inner membrane translocation and laterally released into the lipid phase[5,6,8,9,10]. A Tim21-containing (TIM23SORT) form that is motor free and able to insert proteins laterally into the membrane upon reconstitution and a TIM23MOTOR form lacking Tim[21], but instead associated with the motor complex to enable matrix translocation[30,31] It remains unknown, if the motorcontaining form of the translocase is solely capable of anterograde transport toward the matrix or lateral transport into the lipid phase

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