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Molecular architecture of the active mitochondrial protein gate

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Science  25 Sep 2015:
Vol. 349, Issue 6255, pp. 1544-1548
DOI: 10.1126/science.aac6428

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Dissecting the mitochondrial entry portal

Mitochondria, the powerhouses of the cell, are mainly composed of proteins made in the cytosol. These newly synthesized proteins need to be imported across the organelle's membrane through dedicated protein import machinery. Shiota et al. have worked out the architecture and mechanism of the mitochondrial protein import channel.

Science, this issue p. 1544

Abstract

Mitochondria fulfill central functions in cellular energetics, metabolism, and signaling. The outer membrane translocator complex (the TOM complex) imports most mitochondrial proteins, but its architecture is unknown. Using a cross-linking approach, we mapped the active translocator down to single amino acid residues, revealing different transport paths for preproteins through the Tom40 channel. An N-terminal segment of Tom40 passes from the cytosol through the channel to recruit chaperones from the intermembrane space that guide the transfer of hydrophobic preproteins. The translocator contains three Tom40 β-barrel channels sandwiched between a central α-helical Tom22 receptor cluster and external regulatory Tom proteins. The preprotein-translocating trimeric complex exchanges with a dimeric isoform to assemble new TOM complexes. Dynamic coupling of α-helical receptors, β-barrel channels, and chaperones generates a versatile machinery that transports about 1000 different proteins.

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