Activation of the exchange factor Ras-GRF by calcium requires an intact Dbl homology domain.
Ras-GRF is a guanine nucleotide exchange factor that activates Ras proteins. Its activity on Ras in cells is enhanced upon calcium influx. Activation follows calcium-induced binding of calmodulin to an IQ motif near the N-terminus of Ras-GRF. Ras-GRF also contains a Dbl homology (DH) domain C-terminal to the IQ motif. In many proteins, DH domains act as exchange factors for Rho-GTPase family members. However, we failed to detect exchange activity of this domain on well characterized Rho family members. Instead, we found that mutations analogous to those that block exchange activity of Dbl prevented Ras-GRF activation by calcium/ calmodulin in vivo. All DH domains are followed immediately by a pleckstrin homology (PH) domain. We found that a mutation at a conserved site within the PH domain following the DH domain also prevented Ras-GRF activation by calcium in vivo. These results suggest that in addition to playing a role as activators of Rho proteins, DH domains can also contribute to the coupling of cellular signals to Ras activation.
Freshney
N W
NW
Department of Biochemistry, Tufts University School of Medicine, Boston, MA 02111, USA.
Goonesekera
S D
SD
Feig
L A
LA
D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors; D011485:Protein Binding; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D020663:ras Guanine Nucleotide Exchange Factors; D018631:ras Proteins / Q000378:metabolism*; D020666:ras-GRF1
D002147:Calmodulin; D020662:Guanine Nucleotide Exchange Factors; D011506:Proteins; D011518:Proto-Oncogene Proteins; D020663:ras Guanine Nucleotide Exchange Factors; D020666:ras-GRF1; D019204:GTP-Binding Proteins; D018631:ras Proteins; D002118:Calcium