The GM130 and GRASP65 Golgi proteins cycle through and define a subdomain of the intermediate compartment

Abstract

Integrating the pleomorphic membranes of the intermediate compartment (IC) into the array of Golgi cisternae is a crucial step in membrane transport, but it is poorly understood. To gain insight into this step, we investigated the dynamics by which cis-Golgi matrix proteins such as GM130 and GRASP65 associate with, and incorporate, incoming IC elements. We found that GM130 and GRASP65 cycle via membranous tubules between the Golgi complex and a constellation of mobile structures that we call late IC stations. These stations are intermediate between the IC and the cis-Golgi in terms of composition, and they receive cargo from earlier IC elements and deliver it to the Golgi complex. Late IC elements are transient in nature and sensitive to fixatives; they are seen in only a fraction of fixed cells, whereas they are always visible in living cells. Finally, late IC stations undergo homotypic fusion and establish tubular connections between themselves and the Golgi. Overall, these features indicate that late IC stations mediate the transition between IC elements and the cis-Golgi face.

Death receptor ligation triggers membrane scrambling between Golgi and mitochondria

“…Contrary to HeLa and other adherent cells displaying heterogeneous Golgi staining, 9,11,18 over 90% of untreated Jurkat cells showed a clustered staining of Golgi membranes. However, after 30-40 min of FasL treatment, approx.…”

“…When considering the upper band of its immunoblots, ERGIC53 increased also in light membranes (fraction P20) after Fas activation, suggesting a wide dispersal of the protein (Figure 2aii, right). This redistribution occurred concomitantly with an increased mitochondrial association of GM130, the standard marker of Golgi membranes 18 ( Figure 2ii, cf. Figure 1b), which moved from light membranes normally retained within the cytosol-rich fraction.…”

GRASP65 and GRASP55 Sequentially Promote the Transport of C-terminal Valine-bearing Cargos to and through the Golgi Complex

“…3 Thus, the site of action of this valine-GRASP65 interaction system has to be placed at a post-ER and pre-Golgi station, i.e. the IC, a site where GRASP65 has been shown to recycle from the Golgi complex (31,51). Unfortunately, at present too little is known at the molecular level about cargo protein entry into and transiting through the IC to define in detail the mechanisms promoting anterograde transport of these C-TVM-bearing proteins.…”

“…Unfortunately, at present too little is known at the molecular level about cargo protein entry into and transiting through the IC to define in detail the mechanisms promoting anterograde transport of these C-TVM-bearing proteins. What has so far been established is the compositional heterogeneity of the IC, with its "early" elements that are physically close to but distinct from the ERES, and its "late" elements that are closer to the Golgi complex (31). In this context, active sorting of a cargo protein from the early to the late IC components (through its interaction with GRASP65) would offer a kinetic transport advantage.…”

Models of intracellular transport and evolution of the Golgi complex

“…After segregation, the cargo domain fuses with the medial Golgi, apparently triggering the physical separation of the cargo domain from the IC. The GM130-positive membrane would be segregated and retrieved back into the IC (Marra et al, 2001). One of the possible mechanisms of protein segregation is based on the different thicknesses of membranes along the Golgi stack.…”