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Mol. Cell. Biol., 06 1996, 2689-2699, Vol 16, No. 6
R Foster, KQ Hu, Y Lu, KM Nolan, J Thissen and J Settleman
We have identified a human Rho protein, RhoE, which has unusual structural
and biochemical properties that suggest a novel mechanism of regulation.
Within a region that is highly conserved among small GTPases, RhoE contains
amino acid differences specifically at three positions that confer
oncogenicity to Ras (12, 59, and 61). As predicted by these substitutions,
which impair GTP hydrolysis in Ras, RhoE binds GTP but lacks intrinsic
GTPase activity and is resistant to Rho-specific GTPase-activating
proteins. Replacing all three positions in RhoE with conventional amino
acids completely restores GTPase activity. In vivo, RhoE is found
exclusively in the GTP-bound form, suggesting that unlike previously
characterized small GTPases, RhoE may be normally maintained in an
activated state. Thus, amino acid changes in Ras that are selected during
tumorigenesis have evolved naturally in this Rho protein and have similar
consequences for catalytic function. All previously described Rho family
proteins are modified by geranylgeranylation, a lipid attachment required
for proper membrane localization. In contrast, the carboxy-terminal
sequence of RhoE predicts that, like Ras proteins, RhoE is normally
farnesylated. Indeed, we have found that RhoE in farnesylated in vivo and
that this modification is required for association with the plasma membrane
and with an unidentified cellular structure that may play a role in
adhesion. Thus, two unusual structural features of this novel Rho protein
suggest a striking evolutionary divergence from the Rho family of GTPases.
Copyright © 1996, American Society for Microbiology
Identification of a novel human Rho protein with unusual properties: GTPase deficiency and in vivo farnesylation
Massachusetts General Hospital Cancer Center, Charlestown 02129, USA.
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