Ras and Rap are regulated by different sets of guanine nucleotide exchange factors and GTPase-activating proteins, thus providing one level of specificity.
[2] The identification of Rap1 effector proteins has provided important insights into mechanisms by which Rap1 regulates T-cell receptor (TCR) signaling to integrins.
A constitutively active Rap1 construct, Rap1G12V, was used as a bait in a yeast two-hybrid screen to identify RAPL as a Rap1-binding protein.
This interaction between RAPL and LFA-1 is dependent on lysine residues at positions 1097 and 1099 in the juxtamembrane region of the αL-subunit cytoplasmic domain.
This is a functionally significant region of the αL cytoplasmic domain as deletion of the adjacent GFFKR motif results in a constitutively active LFA-1 integrin (124, 125).
Mutation of these lysine residues to alanine impairs the ability of LFA-1 to redistribute to the leading edge induced by Rap1 activation or overexpression of RAPL.
A striking feature of Rap1 and the Rap1-associated signaling proteins PKD, RAPL, and Mst1 is their localization to membranes where integrins are found.