Involvement of the transmembrane protein p23 in biosynthetic protein transport.
Here, we report the localization and characterization of BHKp23, a member of the p24 family of transmembrane proteins, in mammalian cells. We find that p23 is a major component of tubulovesicular membranes at the cis side of the Golgi complex (estimated density: 12,500 copies/micron2 membrane surface area, or approximately 30% of the total protein). Our data indicate that BHKp23-containing membranes are part of the cis-Golgi network/intermediate compartment. Using the G protein of vesicular stomatitis virus as a transmembrane cargo molecule, we find that p23 membranes are an obligatory station in forward biosynthetic membrane transport, but that p23 itself is absent from transport vesicles that carry the G protein to and beyond the Golgi complex. Our data show that p23 is not present to any significant extent in coat protein (COP) I-coated vesicles generated in vitro and does not colocalize with COP I buds and vesicles. Moreover, we find that p23 cytoplasmic domain is not involved in COP I membrane recruitment. Our data demonstrate that microinjected antibodies against the cytoplasmic tail of p23 inhibit G protein transport from the cis-Golgi network/ intermediate compartment to the cell surface, suggesting that p23 function is required for the transport of transmembrane cargo molecules. These observations together with the fact that p23 is a highly abundant component in the intermediate compartment, lead us to propose that p23 contributes to membrane structure, and that this contribution is necessary for efficient segregation and transport.
Rojo
M
M
Department of Biochemistry, University of Geneva, 1211 Geneva 4, Switzerland.
Pepperkok
R
R
Emery
G
G
Kellner
R
R
Stang
E
E
Parton
R G
RG
Gruenberg
J
J
D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D020126:Brefeldin A; D016466:CHO Cells; D002451:Cell Compartmentation; D002458:Cell Fractionation; D016764:Cell Polarity; D003001:Cloning, Molecular; D020756:Coatomer Protein; D006224:Cricetinae; D003517:Cyclopentanes / Q000494:pharmacology; D018076:DNA, Complementary / Q000235:genetics; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D006056:Golgi Apparatus / Q000187:drug effects / Q000378:metabolism*; D008562:Membrane Glycoproteins; D008565:Membrane Proteins / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D016253:Microscopy, Immunoelectron; D008870:Microtubules / Q000187:drug effects; D008969:Molecular Sequence Data; D015739:Nocodazole / Q000494:pharmacology; D011485:Protein Binding; D018160:Receptors, Cytoplasmic and Nuclear; D017422:Sequence Analysis, DNA; D014759:Viral Envelope Proteins / Q000378:metabolism
C108779:BHKp23 protein, mammalian; D020756:Coatomer Protein; D003517:Cyclopentanes; D018076:DNA, Complementary; C028391:G protein, vesicular stomatitis virus; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D014759:Viral Envelope Proteins; D020126:Brefeldin A; D015739:Nocodazole