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Oligomerization of a trans-Golgi/trans-Golgi network retained protein occurs in the Golgi complex and may be part of
J K Locker1, D J Opstelten, M Ericsson
1Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, The Netherlands.
Abstract:
The mouse hepatitis virus M protein is a triple spanning membrane glycoprotein that, when expressed independently, localizes to trans-Golgi as well as to the trans-Golgi network (TGN). Passage of this protein from the endoplasmic reticulum through the intermediate compartment to the late Golgi and TGN can be conveniently followed by analyzing its O-linked sugars. Using pulse-chase analyses we studied the oligomerization of the M protein in sucrose gradients. The Golgi and TGN forms migrated as large heterogeneous complexes, whereas the endoplasmic reticulum and intermediate compartment forms of the protein appeared to migrate as monomer. Moreover, a mutant of the M protein lacking the 22 COOH-terminal amino acids, that is transported to the plasma membrane, gave rise to similar complexes, albeit smaller in size, that persisted at the plasma membrane. We propose that the trans-Golgi/TGN retention of the MHV-M protein is governed by two mechanisms: oligomerization possibly mediated by the transmembrane domains and binding of its cytoplasmic tail to cellular factors in trans Golgi/TGN.
Insights
Mouse hepatitis virus M protein oligomerization in the Golgi apparatus is key to its retention. This process, involving transmembrane domains and cytoplasmic tail interactions, influences protein trafficking and localization.
Area of Science:
- Virology
- Cell Biology
- Molecular Biology
Background:
- Mouse hepatitis virus (MHV) M protein is a triple-spanning membrane glycoprotein.
- Independently expressed M protein localizes to the trans-Golgi and trans-Golgi network (TGN).
Purpose of the Study:
- To investigate the oligomerization of the MHV M protein during its passage through the secretory pathway.
- To elucidate the mechanisms governing the trans-Golgi/TGN retention of the MHV M protein.
Main Methods:
- Pulse-chase analyses were employed to study protein trafficking and oligomerization.
- Sucrose gradient centrifugation was used to analyze the migration patterns of M protein forms.
- O-linked sugar analysis tracked protein passage from the endoplasmic reticulum to the Golgi and TGN.
Main Results:
- M protein forms in the Golgi and TGN migrated as large, heterogeneous complexes.
- M protein in the endoplasmic reticulum and intermediate compartment existed as monomers.
- A mutant M protein lacking the C-terminal 22 amino acids formed smaller complexes that remained at the plasma membrane.
Conclusions:
- Trans-Golgi/TGN retention of MHV M protein is mediated by oligomerization, potentially involving transmembrane domains.
- Binding of the M protein's cytoplasmic tail to cellular factors in the trans-Golgi/TGN also contributes to its retention.