RAP1B and Platelet Function
Platelets contain multiple low molecular weight GTP-binding proteins which share strong sequence similarity to ras including rap, rac, ral, and rho (Nagata et al., 1989; Polakis et al., 1989). In addition, platelets contain regulatory molecules which both control the hydrolysis of GTP bound to the protein and/or promote the exchange of GDP for GTP (Hart et al., 1991). Surprisingly, platelets do not contain the ras molecule in a significant amount, yet possess high levels of the ras regulatory molecule rasGAP. RasGAP has been shown to bind rapla with high affinity without increasing its GTPase activity (Frech et al., 1990). It is generally accepted that in addition to rasGAP acting as a GTPase activating protein, it may function as the downstream target molecule of ras (Hall, 1990a). For this reason, the role of rasGAP and rapl in platelets is intriguing given that platelets also contain the GTPase activating protein specific for rapl. Recent data has proposed that this complex interaction may play a controling role in platelet signal transduction.
KeywordsGTPase Activate Protein Increase cAMP Level Intrinsic GTPase Activity Phosphotyrosine Residue CAAX Motif
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