M. Esaki et al., Two distinct mechanisms drive protein translocation across the mitochondrial outer membrane in the late step of the cytochrome b(2) import pathway, P NAS US, 96(21), 1999, pp. 11770-11775
Citations number
31
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
The import of cytochrome b(2) into mitochondria consists of two steps, The
translocation of the first part of the presequence across the inner membran
e is coupled with the translocation of the tightly folded heme-binding doma
in across the outer membrane and requires a membrane potential Delta Psi an
d the functions of mitochondrial Hsp70 (mHsp70) in the matrix, Once the hem
e-binding domain has passed the outer membrane, the translocation of the re
st of the polypeptide chain across the outer membrane becomes independent o
f Delta Psi and mHsp70. Here we analyzed the late Delta Psi- and mHsp70-ind
ependent step in the transport of cytochrome bz fusion proteins into the in
termembrane space (IMS), The import of the cytochrome b(2) fusion proteins
containing two protein domains linked by a spacer segment into mitochondria
was arrested at a stage at which one domain folded on each side of the out
er membrane, along the pathway that is consistent with the stop-transfer mo
del. The mature-size form of the translocation intermediate could move acro
ss the outer membrane in both directions, and the stabilization of the prot
ein domain in the IMS promoted the forward translocation. On the other hand
, the intermediate-size form of the translocation intermediate, which retai
ns the anchorage to the inner membrane, was transported into the IMS indepe
ndently of the stability of the protein domain in the IMS. These results su
ggest that two distinct mechanisms, the Brownian ratchet and the anchor dif
fusion mechanisms, can operate for the transmembrane movement of the mature
-size form and the intermediate-size form, respectively, of cytochrome bz s
pecies.