Membrane adhesion dictates Golgi stacking and cisternal morphology

Abstract

Two classes of proteins that bind to each other and to Golgi membranes have been implicated in the adhesion of Golgi cisternae to each other to form their characteristic stacks: Golgi reassembly and stacking proteins 55 and 65 (GRASP55 and GRASP65) and Golgin of 45 kDa and Golgi matrix protein of 130 kDa. We report here that efficient stacking occurs in the absence of GRASP65/55 when either Golgin is overexpressed, as judged by quantitative electron microscopy. The Golgi stacks in these GRASP-deficient HeLa cells were normal both in morphology and in anterograde cargo transport. This suggests the simple hypothesis that the total amount of adhesive energy gluing cisternae dictates Golgi cisternal stacking, irrespective of which molecules mediate the adhesive process. In support of this hypothesis, we show that adding artificial adhesive energy between cisternae and mitochondria by dimerizing rapamycin-binding domain and FK506-binding protein domains that are attached to cisternal adhesive proteins allows mitochondria to invade the stack and even replace Golgi cisternae within a few hours. These results indicate that although Golgi stacking is a highly complicated process involving a large number of adhesive and regulatory proteins, the overriding principle of a Golgi stack assembly is likely to be quite simple. From this simplified perspective, we propose a model, based on cisternal adhesion and cisternal maturation as the two core principles, illustrating how the most ancient form of Golgi stacking might have occurred using only weak cisternal adhesive processes because of the differential between the rate of influx and outflux of membrane transport through the Golgi.tethers | GRASPs T he Golgi apparatus plays a central role in the processing, sorting, and secretion of various cargo molecules destined for various intracellular and extracellular destinations (1). In animal and plant cells, its unique structure of four to six stacked, roughly planar cisternae serves, among other things, as a platform to organize Golgi resident glycosyltransferases into distinct membrane-bound subcompartments (the cis-, medial-, and trans-Golgi cisternae) for proper and sequential posttranslational maturation of the transiting cargo proteins (2, 3).Although these characteristic features of Golgi morphology have drawn the attention of many researchers for many decades, the molecular mechanisms underlying them are still unclear (4). Pioneering functional reconstitution studies using a cell-free system in which Golgi stacks (but not ribbons) reassemble from mitotic extracts (5-8) yielded two classes of purified proteins, each clearly contributing to stacking: globular Golgi reassembly and stacking proteins (GRASPs; the homologous proteins GRASP65 and GRASP55) (7, 9) and the helical rod-like and partially homologous proteins Golgi matrix protein of 130 kDa (GM130) and Golgin of 45 kDa (Golgin45) (10, 11). One member of each family (GRASP65 and GM130) is located in the cis-most cisterna (7, 12), and another member of each family (GRASP5...

Golgi apparatus self-organizes into the characteristic shape via postmitotic reassembly dynamics

“…Thus, membrane adhesion basically acts as the flattening force. Lee et al (11) reported that a knockdown of adhesion proteins caused a swelling of Golgi cisternae. In contrast, our simulations indicated that stronger adhesion affecting the membrane morphology prevents the formation of fine Golgi-like strictures (Fig.…”

“…Via the fragmentation, Golgi components completely decompose and lose their morphological characteristics such as the structural anisotropy and long-range coherence. In contrast, there are few reports of moderately decomposed states (11). Therefore, this all-or-none response is a fundamental characteristic of the Golgi architecture.…”

The Golgi apparatus: insights from filamentous fungi

“…It has been proposed that existence of either one or the other Golgi organization reflects the underlying differences in the organization of the endoplasmic reticulum (ER) exit sites: In P. pastoris, where the Golgi forms stacks, ER exit sites are discrete, confined at specific ER locales, while in S. cerevisiae, where the Golgi is dispersed, vesicles bud throughout the ER network (Rossanese et al 1999). Golgins, large coiled-coil proteins at Golgi's cytoplasmic surface, together with Golgi ReAssembly Stacking Proteins (GRASPs) also have been implicated in Golgi stacking, as well as in Golgi ribbon formation in mammalian cells (Wang et al 2003, Munro 2011a, Lee et al 2014, Veenendaal et al 2014, while these proteins are thought to contribute to the specificity of membrane traffic to the Golgi in yeast but also in higher eukaryotes (Behnia et al 2007, Wong andMunro 2014). Nevertheless, the exact mechanism by which stacking is achieved is not definitively understood and even less clear remains the role this Golgi organization plays in protein secretion or other cellular function (Emr et al 2009).…”

JNK2 controls fragmentation of the Golgi complex and the G2/M transition through phosphorylation of GRASP65

“…The unlinking of the Golgi ribbon in G2 is controlled by the protein CtBP1 (also known as, and hereafter referred to as BARS) (Colanzi et al, 2007) and by the Golgi stacking factors GRASP55 (also known as GORASP2) and GRASP65 (also known as GORASP1) (Lee et al, 2014). In this context, BARS stimulates the fission-mediated cleavage of the tubules that connect the stacks of the Golgi ribbon (Carcedo et al, 2004;Corda et al, 2006;Colanzi et al, 2007), and GRASP55 and GRASP65 are involved in the maintenance of the ribbon structure (Puthenveedu and Linstedt, 2004;Sutterlin et al, 2005;Tang et al, 2012;Jarvela and Linstedt, 2014).…”