κB‐Ras proteins are fast‐exchanging GTPases and function via nucleotide‐independent binding of Ral GTPase‐activating protein complexes

Contrary to previous predictions, we provide evidence that the small GTPase κB-Ras possesses intrinsic hydrolytic activity. However, low nucleotide affinity leads to fast nucleotide exchange and renders κB-Ras constitutively GTP-bound in cells. We characterize κB-Ras mutations occurring in tumors and define that nucleotide binding supports protein stability but is not re quired for a constitutive noneffector interaction with RalGAP complexes. κB-Ras (NF-κB inhibitor-interacting Ras-like protein) GTPases are small Ras-like GTPases but harbor interesting differences in important sequence motifs. They act in a tumor-suppressive manner as negative regulators of Ral (Ras-like) GTPase and NF-κB signaling, but little is known about their mod e of function. Here, we demonstrate that, in contrast to predictions based on primary structure, κB-Ras GTPases possess hydrolytic activity. Combined with low nucleotide affinity, this renders them fast-cycling GTPases that are predominantly GTP-bound in cells. We characterize the impact of κB-Ras mutations occurring in tumors and demonstrate that nucleotide binding affects κB-Ras stability but is not strictly required for RalGAP (Ral GTPase-activating protein) binding. This demonstrates that κB-Ras control of RalGAP/Ral signaling occurs in a nucleotide-binding- and switch-independent fas hion.

Source: FEBS Letters - April 12, 2024 Category: Biochemistry Authors: Ren é Rasche, Lisa Helene Apken, Esther Michalke, Daniel Kümmel, Andrea Oeckinghaus Tags: Research Letter Source Type: research