Mitochondrial Membranes Restitution Proceeds via Vesicular Import from ER and Cytosol. Counterparts’ Resemblances and Variances in Mitochondria and Golgi Pathways

Amalia Slomiany,Bronislaw L Slomiany

doi:10.4236/abc.2017.71001

Abstract

The processes of mitochondrial restitution are controlled by nuclear genes that encode proteins synthesized in ER and cytosol and delivered as organelle- and membrane-specific transport vesicles. The analysis of the transporters recovered from inner mitochondrial space (Mitosol) revealed that the ER-synthesized mitochondria-specific transport vesicles consist of two carriers, one remaining in outer mitochondrial membrane (OMM), and the other that transfers specific membrane segments to the inner mitochondrial membrane (IMM). The ER-assembled and IMM-committed membrane segments, while first integrated into OMM, undergo intra-mitochondrial lipid modification reflected in the synthesis of cardiolipin (CL) and inversion into Mitosol with load of IMM associated cytosolic proteins. Then, the CL-bedecked vesicles are released from OMM to Mitosol and upon contact with IMM fuse with the membrane, and the release of cytosolic cargo ensues. While ER-assembled mitochondria-specific transport vesicles fuse with OMM with the aid of the cytosolic, phosphatidylglycerol (PG)-specific phospholipase A2 (PLA2), the Mitosol-contained CL-specific PLA guides vesicles fusion with IMM. The described path of translocation of the membrane segments and the cytosol synthesized proteins into the designated mitochondrial compartments sustains growth and identity of OMM, IMM, maintains protein delivery for intra-mitochondrial lipid and protein modification in Mitosol, and ensures conformity of the cytosolic proteins cargo delivered to matrix.

Highlights

In line with the concept of cell organelles discrete specificity, the fidelity of their restitution and accuracy in retaining their function, are most essential and command processes that are exquisite for every cellular compartment [1]-[9]
The presented results embody continuation of the investigations into transport of mitochondria-destined proteins encoded by nuclear genes and synthesized as proteins intercalated into endoplasmic reticulum (ER) membranes [2] [5], and as translation products of cytosolic ribosomes [29]
The fusion process of the ER-mitochondrial transport vesicles with the outer mitochondrial membrane has not generated any changes in OMM lipid composition, and as illustrated earlier [5] the OMM after fusion with ER-mitochondrial vesicles, consisted of PC, PE, phosphatidic acid (PA), PG and traces of phosphatidylglycerol phosphate (PGP)

Summary

Introduction

In line with the concept of cell organelles discrete specificity, the fidelity of their restitution and accuracy in retaining their function, are most essential and command processes that are exquisite for every cellular compartment [1]-[9]. The features of the currently advocated import pathways stipulate the recognition of the cellular location mediated by the import apparatus, recognition of the docking sites for the incoming replacement elements, generation of translocation channels by incoming membrane associated protein, and conformity of the transferred components [28] Theoretically these features fulfill exquisite demands regarding import devices, the final probes tailored exclusively from the outer- or inner mitochondrial membrane (OMM and IMM, respectively) proteins without the membrane’s-specific lipids, their insertion into proper site of the membrane and the in situ function are doubtful. The concept of engaging the translocase protein sets, which are not shielded from mixture of other cytosol genomic products, assembled for similar but not for identical sites, raises concern whether the precision required for the translocation of the substrates is achieved

Methods

Results

Conclusion