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Golgi Matrix Proteins
The Golgi apparatus is a stack of membrane-bound, flattened compartments called cisternae .
Each cisterna contains a different set of enzymes, making each Golgi compartment distinct.
The tightly packed cisternae are held together by Golgi matrix proteins.
Tubular Golgi matrix or GM proteins and Golgi reassembly stacking proteins or GRASPs connect adjacent cisternae, providing structural integrity to the Golgi stack.
Other matrix proteins called golgins form long chains extending 100 to 400 nanometers from the surface of the Golgi stack to help tether incoming vesicles.
During cell division, GM proteins are phosphorylated by mitotic protein kinases causing the Golgi to fragment and disperse throughout the cytosol.
When the cell divides, the fragments are evenly distributed in the daughter cells. Once the GM proteins are dephosphorylated by protein phosphatases, they reassemble the Golgi fragments into Golgi stacks.
17.16:
Golgi Matrix Proteins
Golgi matrix proteins are a group of highly dynamic proteins that maintain the stacked structure of Golgi. These proteins adapt to rapid morphological changes of the Golgi during the cell cycle. During cell division, mild proteolysis removes these connections resulting in Golgi unstacking. In The daughter cells, these proteins help reassemble the unstacked Golgi.
One of the first identified Golgi matrix proteins was GM130, a rod-like protein located in the cis-Golgi. Subsequently, many Golgi matrix proteins have been discovered, such as Golgi reassembly stacking proteins (GRASPs) and golgins.
GRASPs are peripheral membrane proteins on the cytoplasmic side of the Golgi cisternae that glue together adjacent cisternae like a ribbon. They form oligomers in the tight gaps between cisternae and are regulated by phosphorylation. During cell division, phosphorylation and dephosphorylation of these proteins help in Golgi stack disassembly and reassembly. Additionally, they participate in various cellular processes such as cargo-specific transport, apoptosis, regulation of cell cycle, and microtubule organization.
Golgins are peripheral proteins containing coiled-coil domains anchored on the Golgi membrane. The coiled-coil domains allow them to tether the membranes even over relatively long distances. Flexible regions between the coiled coils allow conformational changes while bringing two membranes close in the stack. Thus, they play a crucial role in maintaining the Golgi structure.
Suggested Reading
- Xiang, Y., & Wang, Y. (2011). New components of the Golgi matrix. Cell and tissue research, 344(3), 365-379.
- Vivero-Salmerón, G., Ballesta, J., & Martínez-Menárguez, J. A. (2008). Heterotypic tubular connections at the endoplasmic reticulum–Golgi complex interface. Histochemistry and cell biology, 130(4), 709-717.