ARHGEF7

Rho guanine nucleotide exchange factor 7 is a protein that in humans is encoded by the ARHGEF7 gene.

ARHGEF7 is commonly known as the p21-activated protein kinase exchange factor beta (beta-PIX or βPIX), because it was identified by binding to p21-activated kinase (PAK) and also contains a guanine nucleotide exchange factor domain.

Domains and functions

βPIX is a multidomain protein that functions both as a signaling scaffold protein and as an enzyme. βPIX shares this domain structure and signaling function with the highly similar ARHGEF6/αPIX protein.

βPIX undergoes extensive alternative splicing to generate multiple variant proteins containing or lacking particular protein domains. Adult forms all lack the amino terminal CH domain, and the two major adult variants have alternate carboxyl terminal region (termed β1 and β2): β1 forms contain the coiled-coil trimerization domain and the PDZ-target motif for binding to PDZ proteins (see below), while β2 forms lack both domains and their corresponding functions.

βPIX contains a central DH/PH RhoGEF domain that functions as a guanine nucleotide exchange factor (GEF) for small GTPases of the Rho family, and specifically Rac and Cdc42. Like other GEFs, βPIX can promote both release of GDP from an inactive small GTP-binding protein and binding of GTP to promote its activation.

Signaling scaffolds bind to specific partners to promote efficient signal transduction by arranging sequential elements of a pathway near each other to facilitate interaction/information transfer, and also by holding these partner protein complexes in specific locations within the cell to promote local or regional signaling. In the case of βPIX, its SH3 domain binds to partner proteins with appropriate polyproline motifs, and particularly to group I p21-activated kinases (PAKs) (PAK1, PAK2 and PAK3).