Ionic control of small GTPase HRas using calmodulin.

HRas is a small GTPase that plays physiologically important roles in various intracellular signal transduction processes, such as cell growth and proliferation. The structure and action mechanisms of HRas have been well-characterized, leading to widespread its use as a molecular switch in bionanomachines. calmodulin, a calcium ion-binding protein, acts as an ion-binding molecular switch and activates the target enzymes. We previously demonstrated that the fusion protein of HRas (M13-HRas) with the calmodulin target peptide M13 at the N-terminus of HRas exhibits reversible regulation of GTPase activity and the interaction between M13-HRas and the downstream signaling factor Raf by calcium ions with calmodulin. In this study, we prepared two new HRas fusion proteins with the M13 peptide at the C-terminus (HRas-M13) and both termini (M13-HRas-M13) of HRas and analyzed the calcium-dependent regulation of HRas function. M13-HRas-M13 more efficiently controlled GTPase, interaction with Raf, and the HRas regulator GEF by calcium ions with calmodulin.