Molecular chaperone function of Mia40 triggers consecutive induced folding steps of the substrate in mitochondrial protein import.
Several proteins of the mitochondrial intermembrane space are targeted by internal targeting signals. A class of such proteins with α-helical hairpin structure bridged by two intramolecular disulfides is trapped by a Mia40-dependent oxidative process. Here, we describe the oxidative folding mechanism underpinning this process by an exhaustive structural characterization of the protein in all stages and as a complex with Mia40. Two consecutive induced folding steps are at the basis of the protein-trapping process. In the first one, Mia40 functions as a molecular chaperone assisting α-helical folding of the internal targeting signal of the substrate. Subsequently, in a Mia40-independent manner, folding of the second substrate helix is induced by the folded targeting signal functioning as a folding scaffold. The Mia40-induced folding pathway provides a proof of principle for the general concept that internal targeting signals may operate as a folding nucleus upon compartment-specific activation.
Magnetic Resonance Center, University of Florence, Via Luigi Sacconi 6, 50019 Sesto Fiorentino, Florence, Italy. banci@cerm.unifi.it
Lucia
L
Banci
Ivano
I
Bertini
Chiara
C
Cefaro
Lucia
L
Cenacchi
Simone
S
Ciofi-Baffoni
Isabella Caterina
IC
Felli
Angelo
A
Gallo
Leonardo
L
Gonnelli
Enrico
E
Luchinat
Dionisia
D
Sideris
Kostas
K
Tokatlidis
D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D000079922:Copper Transport Proteins; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins / Q000737:chemistry / Q000378:metabolism*; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D008956:Models, Chemical; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000737:chemistry / Q000378:metabolism*; D046912:Multiprotein Complexes / Q000737:chemistry / Q000378:metabolism*; D019906:Nuclear Magnetic Resonance, Biomolecular; D017510:Protein Folding; D021381:Protein Transport / Q000502:physiology*
C507282:CHCHD4 protein, human; C491006:COX17 protein, human; D002352:Carrier Proteins; D000079922:Copper Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D018832:Molecular Chaperones; D046912:Multiprotein Complexes