Heterotrimeric G protein αi2 Sequesters RasGAP to Control Neutrophil Sensitivity and Chemotaxis

Abstract

G protein-coupled receptors (GPCRs) direct neutrophil chemotaxis through heterotrimeric G proteins, yet the downstream effectors of the predominant Gai isoform, Gai2, remain incompletely defined. Here we identify the Ras GTPase-activating protein CAPRI (RASA4) as a functional effector of Gai2 that links GPCR signaling to Ras adaptation. Using AlphaFold3-based structural modeling and binding free-energy calculations and experimental verification, we reveal that constitutively active and structurally altered Gai2 mutants (Q205L and T182A) exhibit enhanced binding to CAPRI. Neutrophils expressing these mutants display elevated basal Ras activity, heightened sensitivity to chemoattractant, and improved chemotaxis in low- or subsensitive-concentration gradients. However, these cells exhibit excessive Ras activation and impaired chemotaxis at high, saturating chemoattractant concentrations, while maintaining near-normal responses at intermediate concentrations. These results reveal an upward shift in the concentration range for efficient chemotaxis. Our findings not only establish a previously unrecognized Gai2-CAPRI signaling axis that tunes Ras adaptation but also define a mechanism by which heterotrimeric G proteins calibrate leukocyte navigation across diverse chemoattractant gradients.