
P-Rex1, a guanine nucleotide exchange factor (GEF) for Rac, is synergistically activated by PIP3 and Gβγ subunits, but its regulation remains poorly understood. The study reveals that IP4 inhibits P-Rex1 activity by inducing a conformational change where the pleckstrin homology (PH) domain occludes the active site of the Dbl homology (DH) domain, stabilized by interactions between the DEP1 and DH domains, and between the PH domain and a 4-helix bundle subdomain.


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PIP3-dependent Rac exchanger 1 (P–Rex1) is abundantly expressed in neutrophils and plays central roles in chemotaxis and cancer metastasis by serving as a guanine nucleotide exchange factor (GEF) for Rac. The enzyme is synergistically activated by PIP3 and the heterotrimeric Gβγ subunits, but mechanistic details remain poorly understood. While investigating the regulation of P–Rex1 by PIP3, we discovered that Ins(1,3,4,5)P4 (IP4) inhibits P–Rex1 activity and induces large decreases in backbone dynamics in diverse regions of the protein. Cryo–electron microscopy analysis of the P–Rex1·IP4 complex revealed a conformation wherein the pleckstrin homology (PH) domain occludes the active site of the Dbl homology (DH) domain. This configuration is stabilized by interactions between the first DEP domain (DEP1) and the DH domain and between the PH domain and a 4–helix bundle (4HB) subdomain that extends from the C–terminal domain of P–Rex1. Disruption of the DH—DEP1 interface in a DH/PH–DEP1 fragment enhanced activity and led to a more extended conformation in solution, whereas mutations that constrain the occluded conformation led to decreased GEF activity. Variants of full–length P–Rex1 in which the DH—DEP1 and PH—4HB interfaces were disturbed exhibited enhanced activity during chemokine–induced cell migration, confirming that the observed structure represents the autoinhibited state in living cells. Interactions with PIP3–containing liposomes led to disruption of these interfaces and increased dynamics protein–wide. Our results further suggest that inositol phosphates such as IP4 help to inhibit basal P–Rex1 activity in neutrophils, similar to their inhibitory effects on phosphatidylinositol–3–kinase.

### Competing Interest Statement

The authors have declared no competing interest.

Structural and dynamic changes in P-Rex1 upon activation by PIP3 and inhibition by IP4

structural-and-functional-insights-into-the-regulation-of-p-rex1-a-key-regulator-of-neutrophil-chemotaxis-and-cancer-metastasis


Structural and Functional Insights into the Regulation of P-Rex1, a Key Regulator of Neutrophil Chemotaxis and Cancer Metastasis
