Saccharomyces cerevisiae Rab-GDI Displacement Factor Ortholog Yip3p Forms Distinct Complexes with the Ypt1 Rab GTPase and the Reticulon Rtn1p

Abstract

Rab GTPases are crucial regulators of organelle biogenesis, maintenance, and transport. Multiple Rabs are expressed in all cells, and each is localized to a distinct set of organelles, but little is known regarding the mechanisms by which Rabs are targeted to their resident organelles. Integral membrane proteins have been postulated to serve as receptors that recruit Rabs from the cytosol in a complex with the Rab chaperone, GDI, to facilitate the dissociation of Rab and GDI, hence facilitating loading of Rabs on membranes. We show here that the yeast (Saccharomyces cerevisiae) Golgi Rab GTPase Ypt1p can be copurified with the integral membrane protein Yip3p from detergent cell extracts. In addition, a member of the highly conserved reticulon protein family, Rtn1p, is also associated with Yip3p in vivo. However, Ypt1p did not copurify with Rtn1p, indicating that Yip3p is a component of at least two different protein complexes. Yip3p and Rtn1p are only partially colocalized in cells, with Yip3p localized predominantly to the Golgi and secondarily to the endoplasmic reticulum, whereas Rtn1p is localized predominantly to the endoplasmic reticulum and secondarily to the Golgi. Surprisingly, the intracellular localization of Rabs was not perturbed in yip3⌬ or rtn1⌬ mutants, suggesting that these proteins do not play a role in targeting Rabs to intracellular membranes. These data indicate that Yip3p may have multiple functions and that its interaction with Rabs is not critical for their recruitment to organelle membranes.

An Arabidopsis Prenylated Rab Acceptor 1 Isoform, AtPRA1.B6, Displays Differential Inhibitory Effects on Anterograde Trafficking of Proteins at the Endoplasmic Reticulum

“…To gain insight into the physiological role of AtPRA1.B6, the effect of high expression levels of AtPRA1.B6 on anterograde trafficking of various cargo proteins was examined. In a previous study, overexpression of Yip3 in yeast resulted in an inhibition of anterograde trafficking (Geng et al, 2005). A similar observation was made when Yip6b/GTRAP3-18 was expressed in animal cells (Ruggiero et al, 2008).…”

“…Furthermore, overexpression of Yip3p causes ER membrane proliferation, a well-known phenotype resulting from the inhibition of anterograde trafficking at the ER (Kaiser and Schekman, 1990). These results raise the possibility that Yip3p plays a role in the biogenesis of coat protein complex II (COP II) vesicles at the ER in yeast (Geng et al, 2005). Thus, the biological role of PRA1 has not been fully characterized.…”

“…The inhibition of anterograde trafficking by high levels of AtPRA1.B6 homologs is not unique to plants. Similarly, overexpression of yeast and animal homologs, Yip3p and Yip6b, respectively, inhibits ER-to-Golgi transport in yeast and animal cells (Geng et al, 2005;Ruggiero et al, 2008). In addition, the overexpression of JM4/Yip6a suppresses the trafficking of the CC chemokine receptor 5 to the cell surface (Schweneker et al, 2005).…”

“…In addition, when HA:AtPRA1.B6 was expressed at high levels, it localized to the ER and the Golgi apparatus. Yeast Yip3, the likely ortholog of AtPRA1, exhibits similar localization patterns, with a primary localization to the Golgi apparatus and a minor portion to the ER (Geng et al, 2005). To gain insight into the physiological role of AtPRA1.B6, the effect of high expression levels of AtPRA1.B6 on anterograde trafficking of various cargo proteins was examined.…”

Hyphal and cytoskeleton polarization in Tuber melanosporum: A genomic and cellular analysis

“…It has been reported that Pra1 protein has a large COOH-terminal hydrophobic region, and it binds multiple Rabs (Calero et al, 2002) and that catalyzes the dissociation of endosomal Rab-Gdi complexes in S. cerevisiae ( Sivars et al, 2003). In S. cerevisiae, the overexpression of Yip3p (Pra1p) inhibits cellular growth, and it can play a crucial role in vesicles trafficking ( Geng et al, 2005).…”