An Electron Tomographic Analysis of Giantin-Deficient Golgi Proposes a New Function of the Golgin Protein Family.

ABSTRACT

The Golgi apparatus is an organelle that mediates modifications, sorting, and transport of proteins and lipids. Golgins are a group of proteins with coiled-coil structures that localize to the Golgi and are thought to function as tethers to facilitate the docking of vesicles, Rab GTPases, and cytoskeleton components to the Golgi stack. Giantin is the longest golgin and has been thought to function as a tether for COPI vesicles along with other golgins, such as p115 and GM130. Contrary to our expectation that the loss of the tether will result in an increase in untethered COPI vesicles in the cytoplasm, our electron microscopy observations showed that the fenestrae normally present in Golgi cisternae were reduced upon Giantin knockdown. We also found that this structural change is accompanied by altered secretion of cargo proteins and cell surface glycosylation. These results indicate that there exists a correlation between Golgi structural changes caused by the loss of Giantin and Golgi function. Here, we describe electron tomography methods for the detection of structural changes in the Golgi.