Abstract
Previously we showed that smooth microsomes from a variety of tissues effectively cleaved, sequestered, and "core" glycosylated nascent chains of secretory proteins. To further characterize the role of smooth membranes in the biosynthesis of secretory polypeptides, rat liver smooth microsomes were separated into smooth endoplasmic reticulum and Golgi fractions. Membranes of the smooth endoplasmic reticulum cleaved the signal peptide of pre-placental lactogen, attached the high mannose core to the alpha subunit of chorionic gonadotropin, and sequestered the processed proteins. None of these processing steps were performed by Golgi membranes. However, processing of asparagine-linked oligosaccharides and the coincident addition of terminal sugars was performed by Golgi but not by smooth endoplasmic reticulum membranes. The properties of this post-translational reaction are very similar to those described for the reactions in vivo. These observations demonstrate that the enzymes for co-translational (pre-protein processing) and posttranslational (oligosaccharide maturation) processing events are localized in the endoplasmic reticulum and Golgi apparatus, respectively. This functional differentiation of Golgi and endoplasmic reticulum membranes is an important feature of the secretory process in eukaryotic cells. Restriction of the recognition and transport of nascent secretory proteins to the endoplasmic reticulum establishes the polarity necessary for the ordered sequence of post-translational steps involved in the synthesis and maturation of secretory proteins.
Highlights
Membranes of the smooth endoplasmic reticulum in SER
Smooth microsomes isolated from Krebs’ I1 ascites tumor cells and bovine adrenal cortex processed and translocated nascent chains of hPL and hCGa very efficiently.Both of these tissues contain significantly less RER than is found in rat liver, providing strong evidence that the processing properties of this post-translational reaction are very observed with smooth microsomesis not due to contamination similar to those described for the reactions in vivo. by stripped RER that may have formed during membrane
We describe a cellfree assay for the Golgi-dependent modification of the high mannose oligosaccharide added to hCGa in the ER
Summary
We have recently shown that smooth micleaved the signal peptide of pre-placental lactogen, attached the high mannose core to the a subunit of chorionicgonadotropin, and sequestered the processed proteins. Noneof these processing steps were performed by Golgi membranes. Smooth microsomes isolated from Krebs’ I1 ascites tumor cells and bovine adrenal cortex processed and translocated nascent chains of hPL and hCGa very efficiently.Both of these tissues contain significantly less RER than is found in rat liver, providing strong evidence that the processing properties of this post-translational reaction are very observed with smooth microsomesis not due to contamination similar to those described for the reactions in vivo. Restriction of the recognition and transport of nascent secretory proteins to the endoplasmic reticulum establishes the polarity necessary for the ordered sequence of post-translational steps involved in the synthesis and maturation of secretory proteins
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
