title: The membrane proteins TRAMp and sec61 alpha p may be involved in post-translational transport of presecretory proteins into mammalian microsomes.
abstract: The presecretory protein ppcecDHFR, a hybrid between preprocecropinA and dihydrofolate reductase, is transported into mammalian microsomes post-translationally, i.e. independent of ribosome and signal recognition particle. Here, the involvement of microsomal proteins in ribonucleoparticle-independent transport of ppcecDHFR was analyzed by transport into trypsin-pretreated microsomes and by transport of a truncated version of ppcecDHFR and subsequent chemical cross-linking. We observed that post-translational transport of ppcecDHFR can occur into microsomes which had been pretreated with trypsin (final concentration, 100 micrograms/ml) and that of the known transport components only TRAMp and sec61 alpha p are still present under these conditions. Furthermore, we found that the truncated ppcecDHFR, ppcecDHFR-98mer', can be cross-linked to 36 kDa microsomal membrane proteins during post-translational transport. Therefore, the two microsomal membrane proteins with molecular masses of about 36 kDa, TRAMp and sec61 alpha p, appear to be involved in the post-translational transport of ppcecDHFR and ppcecDHFR-98mer.
authors.affiliation: Institut für Biochemie und Molekulare Zellbiologie, Universität Göttingen, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Klappa
authors.forename: M
authors.initials: M
authors.lastname: Zimmermann
authors.forename: R
authors.initials: R
authors.lastname: Zimmermann
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D004285:Dogs; D005033:Ethylmaleimide / Q000494:pharmacology; D066298:In Vitro Techniques; D007301:Insect Hormones / Q000378:metabolism; D019476:Insect Proteins; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism*; D011498:Protein Precursors / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D000069816:SEC Translocation Channels; D013762:Tetrahydrofolate Dehydrogenase / Q000378:metabolism; D014357:Trypsin
chemical_list: C059037:CecA2 protein, Bombyx mori; D007301:Insect Hormones; D019476:Insect Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D011498:Protein Precursors; D011993:Recombinant Fusion Proteins; D000069816:SEC Translocation Channels; C074282:translocating chain-associating membrane protein (TRAM); D000255:Adenosine Triphosphate; D013762:Tetrahydrofolate Dehydrogenase; D014357:Trypsin; D005033:Ethylmaleimide