Ca. Lancaster et al., CHARACTERIZATION OF RHOGAP - A GTPASE-ACTIVATING PROTEIN FOR RHO-RELATED SMALL GTPASES, The Journal of biological chemistry, 269(2), 1994, pp. 1137-1142
GTPase-activating proteins or GAPs play an important role in signal tr
ansduction pathways regulated by GTP-binding proteins. In addition to
acting as down-regulators of GTPases, there is growing evidence that t
hey also act as effector molecules required for downstream signaling.
PLC-beta1, the target protein regulated by the heterotrimeric GTPase G
q, has been shown to be a GAP, whereas rasGAP, a down-regulator of the
small GTPase ras, may be required for ras-mediated signals. We have p
urified a GAP specific for the rho subfamily of small GTPases. Partial
sequence analysis of rhoGAP has led to the identification of a family
of related proteins which now includes bcr, chimaerin, p190, p85, and
3BP-1. We report here the isolation of a cDNA clone encoding human rh
oGAP and the expression of recombinant protein. The full-length protei
n is 50 kDa and is ubiquitously expressed in mammalian cells. At least
three members of the rho family are substrates for rhoGAP, rho, rac,
and G25K/CDC42, and they each bind equally well to the protein. In vit
ro GTPase assays, however, reveal that G25K/CDC42 is the preferred sub
strate. RhoGAP contains a proline-rich sequence, suggesting that it is
an SH3-binding protein.