'Piggy-back' transport of Xenopus hyaluronan synthase (XHAS1) via the secretory pathway to the plasma membrane.
Hyaluronan is the sole glycosaminoglycan whose biosynthesis takes place directly at the plasma membrane. The mechanism by which hyaluronan synthase (HAS) becomes inserted there, as well as the question of how the enzyme discriminates between particular membrane species in polarized cells, are largely unknown. In vitro translation of HAS suggested that the nascent protein becomes stabilized in the presence of microsomal membranes, but would not insert spontaneously into membranes after being translated in the absence of those. We therefore monitored the membrane attachment of enzymatically active fusion proteins consisting of Xenopus HAS1 and green fluorescent protein shortly after de novo synthesis in Vero cells. Our data strongly suggest that HAS proteins are directly translated on the ER membrane without exhibiting an N-terminal signal sequence. From there the inactive protein is transferred to the plasma membrane via the secretory pathway. For unknown reasons, HAS inserted into membranes other than the plasma membrane remains inactive.
Müllegger
Johannes
J
Institute of Molecular Biology, Austrian Academy of Sciences, Billrothstr. 11, A-5020 Salzburg, Austria.
Rustom
Amin
A
Kreil
Günther
G
Gerdes
Hans-Hermann
HH
Lepperdinger
Günter
G
D000818:Animals; D001693:Biological Transport, Active / Q000502:physiology; D015820:Cadherins / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology; D018076:DNA, Complementary / Q000096:biosynthesis; D005456:Fluorescent Dyes / Q000737:chemistry; D014453:Glucuronosyltransferase / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D016695:Glycosyltransferases; D006056:Golgi Apparatus / Q000378:metabolism; D000076002:Hyaluronan Synthases; D006820:Hyaluronic Acid / Q000096:biosynthesis; D007120:Immunochemistry; D018374:LLC-PK1 Cells; D008565:Membrane Proteins; D008715:Methionine / Q000378:metabolism; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008861:Microsomes / Q000201:enzymology; D010957:Plasmids / Q000235:genetics; D014176:Protein Biosynthesis; D013552:Swine; D014166:Transferases; D014981:Xenopus; D029867:Xenopus Proteins
D015820:Cadherins; D018076:DNA, Complementary; D005456:Fluorescent Dyes; D008565:Membrane Proteins; D029867:Xenopus Proteins; D006820:Hyaluronic Acid; D008715:Methionine; D014166:Transferases; D016695:Glycosyltransferases; D014453:Glucuronosyltransferase; C056944:HAS1 protein, Xenopus; D000076002:Hyaluronan Synthases