Abstract
The Golgi lumenal GDPase plays an important role in the mannosylation of proteins and lipids of Saccharomyces cerevisiae by regulating the amount of GDP-mannose available in the Golgi lumen. The enzyme makes available GMP as an antiporter to be coupled with entry of GDP-mannose into the Golgi lumen from the cytosol. Using radiation inactivation and target analysis, we have now determined the functional molecular mass of the GDPase within the Golgi membrane and whether or not the enzyme has functional associations with other Golgi membrane proteins, including mannosyltransferases and the GDP-mannose transporter. The functional size of the GDPase was found to be approximately twice the estimated structural target size of the protein; this strongly suggests that the GDPase protein in situ functions as homodimer and does not require association with other membrane proteins for its function.
Highlights
From the :j:Department of Biochemistry and Molecular Biology, University of Massachusetts Medical Center, Worcester, Massachusetts 01655-1013 and §Laboratory of Physical Biology, NIAMS, National Institutes of Health, Bethesda, Maryland 20892
The Golgi lumenal GDPase plays an important role in the mannosylation ofproteins and lipids ofSaccharomyces cerevisiae by regulating the amount ofGDP-mannose available in the Golgi lumen
The enzyme makes available GMP as an antiporter to be coupled with entry of GDP-mannose into the Golgi lumen from the cytosol
Summary
From the :j:Department of Biochemistry and Molecular Biology, University of Massachusetts Medical Center, Worcester, Massachusetts 01655-1013 and §Laboratory of Physical Biology, NIAMS, National Institutes of Health, Bethesda, Maryland 20892. Using radiation inactivation and target analysis, we have determined the functional molecular mass of the GDPase within the Golgi membrane and whether or not the enzyme has functional associations with other Golgi membrane proteins, including mannosyltransferases and the GDP-mannose transporter. The addition of mannose to N- and O-linked outer chain oligosaccharides of glycoproteins and mannosylation of glycosphingolipids occurs in the yeast Golgi apparatus lumen (1). These reactions require a mannosyl donor, GDP-mannose, which is synthesized in the cytosol and must be translocated to the Golgi lumen by a specific membrane carrier (2).
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