Structural and Functional Analysis of the Globular Head Domain of p115 Provides Insight into Membrane Tethering

Abstract

Molecular tethers play a central role in the organization of the complex membrane architecture of eukaryotic cells. p115 is a ubiquitous, essential tether involved in vesicle transport and the structural organization of the exocytic pathway. We describe two crystal structures of the N-terminal domain of p115 at 2.0 Å resolution. The p115 structures show a novel α-solenoid architecture constructed of 12 armadillo-like, tether-repeat (TR), α-helical tripod motifs. We find that the H1 TR binds the Rab1 GTPase involved in ER to Golgi transport. Mutation of the H1 motif results in the dominant negative inhibition of ER to Golgi trafficking. We propose that the H1 helical tripod contributes to the assembly of Rab-dependent complexes responsible for the tether and SNARE-dependent fusion of membranes.

The Golgi Protein p115 Associates with γ-Tubulin and Plays a Role in Golgi Structure and Mitosis Progression

“…2A). The existence and nature of this domain has been confirmed by x-ray crystallography studies (42,43). Armadillo repeats have been implicated in interactions between cell adhesion proteins and the cytoskeleton (44).…”

The Eutherian Armcx genes regulate mitochondrial trafficking in neurons and interact with Miro and Trak2

“…These findings suggest that Alex3 regulates aggregation by an as yet unknown mechanism, which is likely to involve interaction with proteins that control tethering and aggregation, including Mitofusins 28 . It has been reported that Arm motifs of p115 protein bind the Rab1 GTPase controlling ER to Golgi trafficking and regulate vesicle tethering 42 . Mitochondrial aggregating phenotypes have been observed after dysfunction of Miro and Trak2 proteins, suggesting that alteration of transport results in aggregation 43,44 .…”

Structure of Golgi Transport Proteins

“…The aminoterminal TR in the p115 head domains interacts with active, membrane-bound Rab1, likely serving to anchor p115 to the membrane (Allan et al 2000;An et al 2009). This interaction has been proposed to tether COP II vesicles to each other in homotypic vesicle fusion (Bentley et al 2006).…”

“…Based on weak sequence similarity, it has also been suggested that the coiled-coil domains of several golgins might be interrupted by tether repeats related to the armadillo-like repeats in the globular head domain of p115 ). The length of the coiled-coil domains of many golgins is enormous: in both giantin and Uso1, for example, they are 150 nm long (Yamakawa et al 1996;An et al 2009). Thus, these golgins would be able to tether incoming vesicles at very long distances.…”