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Post-translational modifications distinguish cell surface from Golgi-retained beta 1,4 galactosyltransferase
R D Teasdale1, F Matheson, P A Gleeson
1Department of Pathology and Immunology, Monash University Medical School, Alfred Hospital, Melbourne, Victoria, Australia.
Glycobiology
|December 1, 1994
Summary
Beta 1,4 Galactosyltransferase (GalT) localization depends on its transmembrane domain. Oligomerization may be key for retaining GalT within the Golgi apparatus, distinguishing it from cell surface-localized proteins.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Beta 1,4 Galactosyltransferase (GalT) is a crucial Golgi-resident enzyme.
- The transmembrane domain of GalT is essential for its proper localization within the Golgi apparatus.
Purpose of the Study:
- To investigate the role of the GalT transmembrane domain in protein localization and post-translational modification.
- To compare the behavior of full-length GalT with a hybrid molecule containing the transferrin receptor's transmembrane domain.
Main Methods:
- Transfection of COS and murine L cells with GalT and GalT/hybrid constructs.
- Analysis of protein localization, molecular mass, and post-translational modifications.
- Use of brefeldin A to study modifications in the trans-Golgi network (TGN).
- Cross-linking studies to assess GalT oligomerization.
Main Results:
- GalT/hybrid molecules showed differential distribution between cell types, with efficient surface expression in COS cells and both Golgi and surface localization in L cells.
- Two glycoprotein products differing by 7 kDa were observed, attributed to TGN-dependent post-translational modifications.
- Higher molecular weight species, indicative of cell surface transport, were more prevalent for the GalT/hybrid protein.
- Full-length GalT primarily formed high-molecular-weight aggregates, suggesting oligomerization is crucial for Golgi retention.
Conclusions:
- Expression levels influence the intracellular distribution of GalT/hybrid proteins.
- Full-length GalT localization involves active retention within the Golgi, not retrieval.
- Oligomerization of GalT may be a prerequisite for its retention in the Golgi apparatus.