J. Biol. Chem., Vol. 265, Issue 1, 9-12, Jan, 1990
An amino-terminal signal sequence abrogates the intrinsic membrane- targeting information of mitochondrial uncoupling protein
XQ Liu, KB Freeman and GC Shore
Department of Biochemistry, McGill University, Montreal, Canada.
Mitochondrial uncoupling protein, a polytopic integral protein of the inner
membrane, is initially made in the cytoplasm as a soluble polypeptide (307
amino acids) lacking a cleavable targeting (signal) peptide. Earlier
studies (Liu, X., Bell, A. W., Freeman, K. B., and Shore, G. C. (1988) J.
Cell Biol. 107, 503-509) identified internal regions of the molecule that
are critical for targeting and membrane insertion. Here, we demonstrate
that the ability of uncoupling protein to insert into the inner membrane is
abrogated when the molecule is fused behind the matrix-targeting signal of
preornithine carbamyltransferase; the hybrid protein was imported across
the inner membrane and deposited in the matrix where it was processed. In
this context, however, the processed product remained in the matrix and was
incapable of inserting into the inner membrane.