The TRAPP Complex: Insights into its Architecture and Function

Abstract

Vesicle-mediated transport is a process carried out by virtually every cell and is required for the proper targeting and secretion of proteins. As such, there are numerous players involved to ensure that the proteins are properly localized. Overall, transport requires vesicle budding, recognition of the vesicle by the target membrane and fusion of the vesicle with the target membrane resulting in delivery of its contents. The initial interaction between the vesicle and the target membrane has been referred to as tethering. Because this is the first contact between the two membranes, tethering is critical to ensuring that specificity is achieved. It is therefore not surprising that there are numerous ‘tethering factors’ involved ranging from multisubunit complexes, coiled-coil proteins and Rab guanosine triphosphatases. Of the multisubunit tethering complexes, one of the best studied at the molecular level is the evolutionarily conserved TRAPP complex. There are two forms of this complex: TRAPP I and TRAPP II. In yeast, these complexes function in a number of processes including endoplasmic reticulum-to-Golgi transport (TRAPP I) and an ill-defined step at the trans Golgi (TRAPP II). Because the complex was first reported in 1998 (1), there has been a decade of studies that have clarified some aspects of its function but have also raised further questions. In this review, we will discuss recent advances in our understanding of yeast and mammalian TRAPP at the structural and functional levels and its role in disease while trying to resolve some apparent discrepancies and highlighting areas for future study.

The Golgi apparatus: insights from filamentous fungi

“…TRAPPI is a demonstrated GEF of Ypt1/ Rab1 (GEFs stimulate GDP release to allow binding of GTP by GTPases and determine Rab GTPases membrane recruitment and the subsequent recruitment of Rab effectors). The physiological role of TRAPPII was controversial: Some data pointed at TRAPPII being the GEF of Ypt31, which suggested that conversion of TRAPPI into TRAPPII at the Golgi would result in a transition from an earlier, Ypt1-containing, to a later, Ypt31-containing, compartment (Sacher et al 2008). However, other studies have showed that in vitro both TRAPPI and II are Ypt1 GEFs (Cai et al 2008), suggesting that one version of TRAPP might activate Ypt1 at the early Golgi, while the other might activate Ypt1 at the late Golgi.…”

“…HypA is a homolog of Trs120, a subunit of the Golgi-related oligomeric transport protein particle (TRAPP) complex. TRAPP comes in two versions, TRAPPI and TRAPPII, the latter deriving from the former by acquisition of three TRAPPIIspecific subunits, Trs120, Trs130 and Trs65 (Sacher et al 2008). TRAPPI is a demonstrated GEF of Ypt1/ Rab1 (GEFs stimulate GDP release to allow binding of GTP by GTPases and determine Rab GTPases membrane recruitment and the subsequent recruitment of Rab effectors).…”

Arabidopsis TRAPPII is functionally linked to Rab-A, but not Rab-D in polar protein trafficking intrans-Golgi network

“…19,[37][38][39] In the case of TRAPPI-mediated COPII tethering, it is believed that the initial tethering requires an interaction between TRAPPI and Sec23, 37 perhaps also an interaction between TRAPPI and Ypt1. 38 It is likely that TRAPPII in plant cells can also serve as RAB-A1c(Q72L).…”

Modular TRAPP Complexes Regulate Intracellular Protein Trafficking Through Multiple Ypt/Rab GTPases in Saccharomyces cerevisiae

“…TRAPP is a multisubunit modular complex (Sacher et al 2008), which exists in at least three forms. TRAPP I, which contains five essential subunits, acts as a GEF for Ypt1 Wang et al 2000), and is required for ER-to-Golgi transport (Sacher et al 1998).…”