This domain is found in RGS9 (Class C) regulator of G-protein signalling (RGS) protein present in Mus musculus. RGS proteins attenuate heterotrimeric G-protein signalling by enhancing the intrinsic GTPase activity of G-alpha subunits and are vital for proper signal transduction kinetics. The domain is referred to as DEP helical extension (DHEX) because it is located next to N-terminal Dishevelled/Egl-10/Pleckstrin homology (DEP) domain. Both the DEP and DHEX domains are necessary, but not sufficient, to bind anchoring proteins such as RGS9 anchor protein. DHEX has no close structural homologs [1]. This domain is also found in regulator of G-protein signaling 7 (RGS7), the crystal structure of which has been solved [2].

1: Crystal structure of the multifunctional Gbeta5-RGS9 complex. Cheever ML, Snyder JT, Gershburg S, Siderovski DP, Harden TK, Sondek J; Nat Struct Mol Biol. 2008;15:155-162. PMID:18204463

2: Structural organization of a major neuronal G protein regulator, the RGS7-Gbeta5-R7BP complex. Patil DN, Rangarajan ES, Novick SJ, Pascal BD, Kojetin DJ, Griffin PR, Izard T, Martemyanov KA; Elife. 2018; [Epub ahead of print] PMID:30540250