Abstract
The flat Golgi cisterna is a highly conserved feature of eukaryotic cells, but how is this morphology achieved and is it related to its function in cargo sorting and export? A physical model of cisterna morphology led us to propose that sphingomyelin (SM) metabolism at the trans-Golgi membranes in mammalian cells essentially controls the structural features of a Golgi cisterna by regulating its association to curvature-generating proteins. An experimental test of this hypothesis revealed that affecting SM homeostasis converted flat cisternae into highly curled membranes with a concomitant dissociation of membrane curvature-generating proteins. These data lend support to our hypothesis that SM metabolism controls the structural organization of a Golgi cisterna. Together with our previously presented role of SM in controlling the location of proteins involved in glycosylation and vesicle formation, our data reveal the significance of SM metabolism in the structural organization and function of Golgi cisternae.
Highlights
The Golgi complex plays a central role in protein processing, sorting and transport (Emr et al, 2009)
The amount of bending energy associated with local curvature deviations is proportional to the local bending rigidity of the membrane (Helfrich, 1973). Both local variations in the amounts of curvature generators present on the membrane and in the bending rigidity of the membrane can influence the morphology of Golgi cisternae. Taking into account these considerations, our aim here is to establish a physical model for the Golgi membrane morphology, with a special focus on understanding the mechanisms by which SM metabolism controls the overall shape of the Golgi cisternae
This prompted us to propose an alternative model that takes into account two contributions that could potentially influence a role in SM-regulated shaping of the Golgi cisternae: (i) the presence of small, rigid, and highly dynamic membrane nanodomains enriched in sphingolipids and cholesterol; and (ii) the SM-dependent recruitment to or release from the Golgi membranes of budding factors and other membrane curvature generators essential for the formation of transport carriers
Summary
The Golgi complex plays a central role in protein processing, sorting and transport (Emr et al, 2009). In higher eukaryotes the Golgi complex consists of multiple stacks of polarized flattened cisternae (Klumperman, 2011). Cisternae polarization allows for the directional transport and sequential processing of newly synthesized proteins arriving at the cis-face of the Golgi complex from the endoplasmic reticulum (Glick and Luini, 2011; Stanley, 2011). A Golgi cisterna consists of two geometrically distinct regions with very different membrane curvatures: the central cisterna part, which is almost flat with the seldom presence of fenestrations or pores; and the highly bent rim of the cisterna. How the different functions of the Golgi membranes (namely, protein processing and transport) are organized between these two regions is not yet fully understood
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
