A multipoint guidance mechanism for ?-barrel folding on the SAM complex.

Mitochondrial ?-barrel proteins are essential for the transport of metabolites, ions and proteins. The sorting and assembly machinery (SAM) mediates their folding and membrane insertion. We report the cryo-electron microscopy structure of the yeast SAM complex carrying an early eukaryotic ?-barrel folding intermediate. The lateral gate of Sam50 is wide ...
open and pairs with the last ?-strand (?-signal) of the substrate-the 19-?-stranded Tom40 precursor-to form a hybrid barrel in the membrane plane. The Tom40 barrel grows and curves, guided by an extended bridge with Sam50. Tom40's first ?-segment (?1) penetrates into the nascent barrel, interacting with its inner wall. The Tom40 amino-terminal segment then displaces ?1 to promote its pairing with Tom40's last ?-strand to complete barrel formation with the assistance of Sam37's dynamic ?-protrusion. Our study thus reveals a multipoint guidance mechanism for mitochondrial ?-barrel folding.
Mesh Terms:
Cryoelectron Microscopy, Mitochondria, Mitochondrial Membrane Transport Proteins, Mitochondrial Precursor Protein Import Complex Proteins, Mitochondrial Proteins, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins
Nat Struct Mol Biol
Date: Feb. 01, 2023
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