TY - JOUR T1 - Cryo-EM structure of the mitochondrial protein-import channel TOM complex from <em>Saccharomyces cerevisiae</em> JF - bioRxiv DO - 10.1101/798371 SP - 798371 AU - Tucker, Kyle AU - Park, Eunyong Y1 - 2019/01/01 UR - http://biorxiv.org/content/early/2019/10/08/798371.abstract N2 - Nearly all mitochondrial proteins are encoded by the nuclear genome and imported into mitochondria following synthesis on cytosolic ribosomes. These precursor proteins are translocated into mitochondria by the TOM complex, a protein-conducting channel in the mitochondrial outer membrane. Using cryo-EM, we have obtained high-resolution structures of both apo and presequence-bound core TOM complexes from Saccharomyces cerevisiae in dimeric and tetrameric forms. Dimeric TOM consists of two copies each of five proteins arranged in two-fold symmetry—Tom40, a pore-forming β-barrel with an overall negatively-charged inner surface, and four auxiliary α-helical transmembrane proteins. The structure suggests that presequences for mitochondrial targeting insert into the Tom40 channel mainly by electrostatic and polar interactions. The tetrameric complex is essentially a dimer of dimeric TOM, which may be capable of forming higher-order oligomers. Our study reveals the molecular organization of the TOM complex and provides new insights about the mechanism of protein translocation into mitochondria. ER -