Abstract
Ras and Rap proteins are closely related small GTPases. Whereas Ras is known for its role in cell proliferation and survival, Rap1 is predominantly involved in cell adhesion and cell junction formation. Ras and Rap are regulated by different sets of guanine nucleotide exchange factors and GTPase-activating proteins, determining one level of specificity. In addition, although the effector domains are highly similar, Rap and Ras interact with largely different sets of effectors, providing a second level of specificity. In this review, we discuss the regulatory proteins and effectors of Ras and Rap, with a focus on those of Rap.
Highlights
Ras and Rap proteins are closely related small GTPases
Ras is central in a network controlling cell proliferation and cell survival, whereas Rap1 predominantly controls cell adhesion, cell junction formation, cell secretion, and cell polarity
The general structural basis of nucleotide exchange by CDC25 homology domains was revealed by the crystal structure of Sos in the presence of Ras [3]
Summary
Small G-proteins are returned to the GDP-bound state by hydrolyzing GTP with the help of GAPs. Ras (Ha-Ras, Ki-Ras, and N-Ras) and Rap proteins (Rap1A, Rap1B, Rap2A, Rap2B, and Rap2C) have similar effector-binding regions that interact predominantly with RA domains or the structurally similar RBDs present in a variety of different proteins. Ras is central in a network controlling cell proliferation and cell survival, whereas Rap predominantly controls cell adhesion, cell junction formation, cell secretion, and cell polarity These different functions are reflected in a largely different set of GEFs and GAPs. the downstream effector proteins operate in a selective manner in either one of the networks. There is a group of GAPs that appears to have a dual specificity for both Ras and Rap, such as several GAP1 (RASAL, CAPRI, and GAPIP4BP) family members and APRIL 24, 2009 VOLUME 284 NUMBER 17
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