In:
Molecular Biology of the Cell, American Society for Cell Biology (ASCB), Vol. 12, No. 8 ( 2001-08), p. 2482-2496
Abstract:
Many mitochondrial outer membrane (MOM) proteins have a transmembrane domain near the C terminus and an N-terminal cytosolic moiety. It is not clear how these tail-anchored (TA) proteins posttranslationally select their target, but C-terminal charged residues play an important role. To investigate how discrimination between MOM and endoplasmic reticulum (ER) occurs, we used mammalian cytochrome b 5 , a TA protein existing in two, MOM or ER localized, versions. Substitution of the seven C-terminal residues of the ER isoform or of green fluorescent protein reporter constructs with one or two arginines resulted in MOM-targeted proteins, whereas a single C-terminal threonine caused promiscuous localization. To investigate whether targeting to MOM occurs from the cytosol or after transit through the ER, we tagged a MOM-directed construct with a C-terminal N-glycosylation sequence. Although in vitro this construct was efficiently glycosylated by microsomes, the protein expressed in vivo localized almost exclusively to MOM, and was nearly completely unglycosylated. The small fraction of glycosylated protein was in the ER and was not a precursor to the unglycosylated form. Thus, targeting occurs directly from the cytosol. Moreover, ER and MOM compete for the same polypeptide, explaining the dual localization of some TA proteins.
Type of Medium:
Online Resource
ISSN:
1059-1524
,
1939-4586
DOI:
10.1091/mbc.12.8.2482
Language:
English
Publisher:
American Society for Cell Biology (ASCB)
Publication Date:
2001
detail.hit.zdb_id:
1474922-1
SSG:
12
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