Many newly synthesized proteins have to become unfolded during translocation across biological membranes. We have analyzed the effects of various stabilization/destabilization mutations in the Ig-like module of the muscle protein titin upon its import from the N terminus or C terminus into mitochondria. The effects of mutations on the import of the titin module from the C terminus correlate well with those on forced mechanical unfolding in atomic-force microscopy (AFM) measurements. On the other hand, as long as turnover of the mitochondrial Hsp70 system is not rate-limiting for the import, import of the titin module from the N terminus is sensitive to mutations in the N-terminal region but not the ones in the C-terminal region that affect resistance to global unfolding in AFM experiments. We propose that the mitochondrial-import system can catalyze precursor-unfolding by reducing the stability of unfolding intermediates.

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Comparative Study | Journal Article | Research Support, Non-U.S. Gov't

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Sato T, Esaki M, Fernandez JM, Endo T

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