Identification and characterization of a new family of guanine nucleotide exchange factors for the Ras-related GTPase Ral

John F. Rebhun, Hongsheng Chen, Lawrence Quilliam

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Abstract

Guanine nucleotide exchange factors (GEFs) are responsible for coupling cell surface receptors to Ras protein activation. Here we describe the characterization of a novel family of differentially expressed GEFs, identified by database sequence homology searching. These molecules share the core catalytic domain of other Ras family GEFs but lack the catalytic non- conserved (conserved non-catalytic/Ras exchange motif/structurally conserved region 0) domain that is believed to contribute to Sos1 integrity. In vitro binding and in vivo nucleotide exchange assays indicate that these GEFs specifically catalyze the GTP loading of the Ral GTPase when overexpressed in 293T cells. A central proline-rich motif associated with the Src homology (SH)2/SH3-containing adapter proteins Grb2 and Nck in vivo, whereas a pleckstrin homology (PH) domain was located at the GEF C terminus. We refer to these GEFs as RalGPS 1A, 1B, and 2 (Ral GEFs with PH domain and SH3 binding motif). The PH domain was required for in vivo GEF activity and could be functionally replaced by the Ki-Ras C terminus, suggesting a role in membrane targeting. In the absence of the PH domain RalGPS 1B cooperated with Grb2 to promote Ral activation, indicating that SH3 domain interaction also contributes to RalGPS regulation. In contrast to the Ral guanine nucleotide dissociation stimulator family of Ral GEFs, the RalGPS proteins do not possess a Ras-GTP-binding domain, suggesting that they are activated in a Ras-independent manner.

Original languageEnglish
Pages (from-to)13406-13410
Number of pages5
JournalJournal of Biological Chemistry
Volume275
Issue number18
DOIs
StatePublished - May 5 2000

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Guanine Nucleotide Exchange Factors
Monomeric GTP-Binding Proteins
Nucleotides
ral Guanine Nucleotide Exchange Factor
Guanosine Triphosphate
ras Guanine Nucleotide Exchange Factors
Chemical activation
ras Proteins
Guanine Nucleotides
src Homology Domains
HEK293 Cells
GTP Phosphohydrolases
Cell Surface Receptors
Sequence Homology
Proline
Catalytic Domain
Assays
Databases
Proteins
Membranes

ASJC Scopus subject areas

  • Biochemistry

Cite this

Identification and characterization of a new family of guanine nucleotide exchange factors for the Ras-related GTPase Ral. / Rebhun, John F.; Chen, Hongsheng; Quilliam, Lawrence.

In: Journal of Biological Chemistry, Vol. 275, No. 18, 05.05.2000, p. 13406-13410.

Research output: Contribution to journalArticle

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