EF-hand, calcium binding motif, found in calumenin
Calumenin, also termed crocalbin, or IEF SSP 9302, is an endo/sarcoplasmic reticulum (ER/SR) resident low-affinity Ca2+-binding protein that contains six EF-hand domains and a C-terminal SR retention signal His-Asp-Glu-Phe (HDEF) tetrapeptide. It is highly expressed in various brain regions. Thus it plays an important role in migration and differentiation of neurons, and/or in Ca2+ signaling between glial cells and neurons. Calumenin is involved in Ca2+ homeostasis through interacting with ryanodine receptor RyR2 and SERCA2. It acts as a novel regulator of SERCA2, and its expressional changes are tightly coupled with Ca2+-cycling of cardiomyocytes. Calumenin also forms a Ca2+-dependent complex with thrombospondin-1, which is broadly involved in haemostasis and thrombosis. Moreover, calumenin is a molecular chaperone that endogenously regulates the vitamin K-dependent gamma-carboxylation of several proteins, including blood coagulation factors (such as FII, FVII, FIX, FX, and proteins C, S and Z), cell survival factors (Gas6) and bone metabolism proteins (such as matrix Gla protein or MGP, osteocalcin and periostin), through targeting the gamma-glutamyl carboxylase. It also functions as a charged F508del-cystic fibrosis transmembrane regulator (CFTR) folding modulator, as well as a G551D-CFTR associated protein. Furthermore, the extracellular calumenin acts as a suppressor of cell migration and tumor metastasis. It binds to and stabilizes fibulin-1, and further inactivates extracellular signal-regulated kinases 1 and 2 (ERK1/2) signaling.
Jiyao W et al.(2023). "The conserved domain database in 2023.",