Cryo-EM Structure of the TOM Core Complex from Neurospora crassa

Abstract

The TOM complex is the main entry gate for protein precursors from the cytosol into mitochondria. We have determined the structure of the TOM core complex by cryoelectron microscopy (cryo-EM). The complex is a 148 kDa symmetrical dimer of ten membrane protein subunits that create a shallow funnel on the cytoplasmic membrane surface. In the core of the dimer, the β-barrels of the Tom40 pore form two identical preprotein conduits. Each Tom40 pore is surrounded by the transmembrane segments of the α-helical subunits Tom5, Tom6, and Tom7. Tom22, the central preprotein receptor, connects the two Tom40 pores at the dimer interface. Our structure offers detailed insights into the molecular architecture of the mitochondrial preprotein import machinery.

Mitochondrial Outer Membrane Channels: Emerging Diversity in Transport Processes

“…The TOM complex contains two or three Tom40 pores that are hold together by Tom22 subunits . The modeled Tom40 β‐barrel fits in its dimension to the pores found in the recent cryo‐electron microscopy structure of the TOM complex …”

“…Structural modeling and in organello folding studies by intramolecular disulfide bond formation reveal that Tom40 forms a 19‐stranded β‐barrel with an N‐terminal α‐helix that is related to VDAC . The TOM complex contains two or three Tom40 pores that are hold together by Tom22 subunits . The modeled Tom40 β‐barrel fits in its dimension to the pores found in the recent cryo‐electron microscopy structure of the TOM complex …”

“…[32][33][34][35] The modeled Tom40 β-barrel fits in its dimension to the pores found in the recent cryo-electron microscopy structure of the TOM complex. [35] Studies of the Tom40 channel provide the first insights how a single channel can translocate a large variety of precursor proteins with different properties. Purified Tom40 forms a cation-selective channel.…”

Cryo-EM structure of the mitochondrial protein-import channel TOM complex from Saccharomyces cerevisiae

“…There are ~1,000-1,500 mitochondrial proteins and the vast 24 majority (~99%) are synthesized by cytosolic ribosomes, initially as precursor proteins that are then 25 imported into mitochondria [1][2][3] . Multiple protein complexes within the organelle mediate membrane 26 translocation and sorting of these precursor polypeptides into four distinct compartments-the outer 27 membrane, the inner membrane, the intermembrane space (IMS), and the matrix. The general import pore 28 in the outer membrane is formed by the TOM complex (Translocase of the Outer Membrane), which is 29 responsible for initial translocation of over 90% of mitochondrial precursor proteins from the cytosol to 30 the IMS.…”

“…Interaction of such presequences (N-terminal cleavable 49 sequences that target ~60-70% mitochondrial precursor proteins) is a key step in translocation 11,[24][25][26] . A 50 cryo-electron microscopy (cryo-EM) structure of an apo form of the core TOM complex from Neurospora 51 crassa was reported 27 , but its relatively low resolution (~7-Å) offered only limited insight and precluded 52 building of an atomic model. In addition, the oligomeric architecture of the TOM complex remained a 53 puzzle.…”