Stromal Cell Derived Factor 4 (SDF4)

Cab45 is ubiquitously expressed, contains an NH2-terminal signal sequence but no membrane-anchor sequences, and binds Ca2+ due to the presence of six EF-hand motifs. Within the superfamily of calcium-binding proteins, it belongs to a recently identified group of proteins consisting of Reticulocalbin and ERC 55 , both of which share significant sequence homology with Cab45 outside the EF-hand motifs. In contrast to reticulocalbin and ERC-55 which are soluble components of the endoplasmic reticulum, Cab45 is a soluble protein localized to the Golgi.

Cab45 is the first calcium- binding protein localized to the lumenal portion of a post-ER compartment; Cab45 is also the first known soluble protein resident in the Golgi lumen.