This is an extracellular domain at the C-terminus of Piezo, or FAM38 mechanosensitive non-specific cation channel proteins. It seems likely that this region of the Piezo proteins may be responsible for R-Ras recruitment because this region is capable of relocalising R-Ras to the ER in eukaryotes.

1: Integrin activation by Fam38A uses a novel mechanism of R-Ras targeting to the endoplasmic reticulum. McHugh BJ, Buttery R, Lad Y, Banks S, Haslett C, Sethi T; J Cell Sci. 2010;123:51-61. PMID:20016066

2: Piezo proteins are pore-forming subunits of mechanically activated channels. Coste B, Xiao B, Santos JS, Syeda R, Grandl J, Spencer KS, Kim SE, Schmidt M, Mathur J, Dubin AE, Montal M, Patapoutian A; Nature. 2012;483:176-181. PMID:22343900