We report the biochemical characterization of Rit and Rin, two members of the Ras superfamily identified by expression cloning. Recombinant Rit and Rin bind GTP and exhibit intrinsic GTPase activity. Conversion of Gln to Leu at position 79 (for Rit) or 78 (for Rin) (equivalent to position 61 in Ras) resulted in a complete loss of GTPase activity. Surprisingly, significant differences were found when the guanine nucleotide dissociation constants of Rit and Rin were compared with the majority of Ras-related GTPases. Both proteins display higher k(off) values for GTP than GDP in the presence of 10 mM Mg2+. These GTP dissociation rates are 5- to 10-fold faster than most Ras-like GTPases. Despite these unique biochemical properties, our data support the notion that both Rit and Rin function as nucleotide-dependent molecular switches. To begin to address whether these proteins act as regulators of distinct signaling pathways, we examined their interaction with a series of known Ras-binding proteins by yeast two-hybrid analysis. Although Rit, Rin, and Ras have highly related effector domain sequences, Rit and Rin were found to interact with the known Ras binding proteins RalGDS, Rlf, and AF-6/Canoe but not with the Raf kinases, RIN1, or the p110 subunit of phosphatidylinositol 3-kinase. These interactions were GTP and effector domain dependent and suggest that RalGDS, Rlf, and AF-6 are Rit and Rin effectors. Their biochemical properties and interaction with a subset of known Ras effector proteins suggest that Rit and Rin may play important roles in the regulation of signaling pathways and cellular processes distinct from those controlled by Ras.
|Number of pages||13|
|Journal||Archives of Biochemistry and Biophysics|
|State||Published - Nov 15 1999|
Bibliographical noteFunding Information:
The nucleotide sequences for human Rit and mouse Rin have been submitted to the Genebank Data Bank with Accession Nos. AF084462 and AF084463. 1 This work was supported in part by National Institutes of Health Grant EY11231. 2Present address: National Institute of Sericultural and Entomological Science 1-2, Ohwashi, Tsukuba, 305 Japan. 3To whom correspondence should be addressed at Department of Biochemistry, College of Medicine, University of Kentucky, 800 Rose St., Lexington, KY 40536-0084. Fax: 606-323-1037. E-mail: email@example.com.
- GTP-binding protein
ASJC Scopus subject areas
- Molecular Biology