Taxonomic distribution of proteins containing VPS9 domains

The tree below includes only several representative species and genera. The complete taxonomic breakdown of all proteins containing VPS9 domains can be accessed here. Click the counts or percentage values to display the corresponding proteins.

Vps9p is a guanine nucleotide exchange factor involved in vesicle-mediated vacuolar protein transport.

Hama H, Tall GG, Horazdovsky BF
J Biol Chem. 1999; 274: 15284-91

Vacuolar protein sorting (vps) mutants of Saccharomyces cerevisiae missort and secrete vacuolar hydrolases. The gene affected in one of these mutants, VPS21, encodes a member of the Sec4/Ypt/Rab family of small GTPases. Rab proteins play an essential role in vesicle-mediated protein transport. Using both yeast two-hybrid assays and chemical cross-linking, we have identified another VPS gene product, Vps9p, that preferentially interacts with a mutant form of Vps21p-S21N that binds GDP but not GTP. In vitro purified Vps9p was found to stimulate GDP release from Vps21p in a dose-dependent manner. Vps9p also stimulated GTP association as a result of facilitated GDP release. However, Vps9p did not stimulate guanine nucleotide exchange of GTP-bound Vps21p or GTP hydrolysis. We tested the ability of Vps9p to stimulate the intrinsic guanine nucleotide exchange activity of Rab5, which is a mammalian sequence homologue of Vps21p, and Ypt7p, which is another yeast Rab protein involved in vacuolar protein transport. Rab5, but not Ypt7p was responsive to Vps9p, which indicates that Vps9p recognizes sequence variation among Rab proteins. We conclude that Vps9p is a novel guanine nucleotide exchange factor that is specific for Vps21p/Rab5. Since there are no obvious Vps9p sequence homologues in yeast, Vps9p may also possess unique regulatory functions required for vacuolar protein transport.

Regulation of the oncogenic activity of BCR-ABL by a tightly bound substrate protein RIN1.

Afar DE, Han L, McLaughlin J, Wong S, Dhaka A, Parmar K, Rosenberg N, Witte ON, Colicelli J
Immunity. 1997; 6: 773-82

RIN1 was originally identified by its ability to physically bind to and interfere with activated Ras in yeast. Paradoxically, RIN1 potentiates the oncogenic activity of the BCR-ABL tyrosine kinase in hematopoietic cells and dramatically accelerates BCR-ABL-induced leukemias in mice. RIN1 rescues BCR-ABL mutants for transformation in a manner distinguishable from the cell cycle regulators c-Myc and cyclin D1 and the Ras connector Shc. These biological effects require tyrosine phosphorylation of RIN1 and binding of RIN1 to the Abl-SH2 and SH3 domains. RIN1 is tyrosine phosphorylated and is associated with BCR-ABL in human and murine leukemic cells. RIN1 exemplifies a new class of effector molecules dependent on the concerted action of the SH3, SH2, and catalytic domains of a cytoplasmic tyrosine kinase.

Protein binding and signaling properties of RIN1 suggest a unique effector function.

Han L, Wong D, Dhaka A, Afar D, White M, Xie W, Herschman H, Witte O, Colicelli J
Proc Natl Acad Sci U S A. 1997; 94: 4954-9

Human RIN1 was first characterized as a RAS binding protein based on the properties of its carboxyl-terminal domain. We now show that full-length RIN1 interacts with activated RAS in mammalian cells and defines a minimum region of 434 aa required for efficient RAS binding. RIN1 interacts with the "effector domain" of RAS and employs some RAS determinants that are common to, and others that are distinct from, those required for the binding of RAF1, a known RAS effector. The same domain of RIN1 that binds RAS also interacts with 14-3-3 proteins, extending the similarity between RIN1 and other RAS effectors. When expressed in mammalian cells, the RAS binding domain of RIN1 can act as a dominant negative signal transduction blocker. The amino-terminal domain of RIN1 contains a proline-rich sequence similar to consensus Src homology 3 (SH3) binding regions. This RIN1 sequence shows preferential binding to the ABL-SH3 domain in vitro. Moreover, the amino-terminal domain of RIN1 directly associates with, and is tyrosine phosphorylated by, c-ABL. In addition, RIN1 encodes a functional SH2 domain that has the potential to activate downstream signals. These data suggest that RIN1 is able to mediate multiple signals. A differential pattern of expression and alternate splicing indicate several levels of RIN1 regulation.

A yeast protein related to a mammalian Ras-binding protein, Vps9p, is required for localization of vacuolar proteins.

Burd CG, Mustol PA, Schu PV, Emr SD
Mol Cell Biol. 1996; 16: 2369-77

In the yeast Saccharomyces cerevisiae, mutations in vacuolar protein sorting (VPS) genes result in secretion of proteins normally localized to the vacuole. Characterization of the VPS pathway has provided considerable insight into mechanisms of protein sorting and vesicle-mediated intracellular transport. We have cloned VPS9 by complementation of the vacuolar protein sorting defect of vps9 cells, characterized its gene product, and investigated its role in vacuolar protein sorting. Cells with a vps9 disruption exhibit severe vacuolar protein sorting defects and a temperature-sensitive growth defect at 38 degrees C. Electron microscopic examination of delta vps9 cells revealed the appearance of novel reticular membrane structures as well as an accumulation of 40- to 50-nm-diameter vesicles, suggesting that Vps9p may be required for the consumption of transport vesicles containing vacuolar protein precursors. A temperature-conditional allele of vps9 was constructed and used to investigate the function of Vps9p. Immediately upon shifting of temperature-conditional vps9 cells to the nonpermissive temperature, newly synthesized carboxypeptidase Y was secreted, indicating that Vps9p function is directly required in the VPS pathway. Antibodies raised against Vps9p immunoprecipitate a rare 52-kDa protein that fractionates with cytosolic proteins following cell lysis and centrifugation. Analysis of the VPS9 DNA sequence predicts that Vps9p is related to human proteins that bind Ras and negatively regulate Ras-mediated signaling. We term the related regions of Vps9p and these Ras-binding proteins a GTPase binding homology domain and suggest that it defines a family of proteins that bind monomeric GTPases. Vps9p may bind and serve as an effector of a rab GTPase, like Vps2lp, required for vacuolar protein sorting.

A human protein selected for interference with Ras function interacts directly with Ras and competes with Raf1.

Han L, Colicelli J
Mol Cell Biol. 1995; 15: 1318-23

The overexpression of some human proteins can cause interference with the Ras signal transduction pathway in the yeast Saccharomyces cerevisiae. The functional block is located at the level of the effector itself, since these proteins do not suppress activating mutations further downstream in the same pathway. We now demonstrate, with in vivo and in vitro experiments, that the protein encoded by one human cDNA (clone 99) can interact directly with yeast Ras2p and with human H-Ras protein, and we have named this gene rin1 (Ras interaction/interference). The interaction between Ras and Rin1 is enhanced when Ras is bound to GTP. Rin1 is not able to interact with either an effector mutant or a dominant negative mutant of H-Ras. Thus, Rin1 displays a human H-Ras interaction profile that is the same as that seen for Raf1 and yeast adenylyl cyclase, two known effectors of Ras. Moreover, Raf1 directly competes with Rin1 for binding to H-Ras in vitro. Unlike Raf1, however, the Rin1 protein resides primarily at the plasma membrane, where H-Ras is localized. These data are consistent with Rin1 functioning in mammalian cells as an effector or regulator of H-Ras.