Penta-EF hand, calcium binding motifs, found in sorcin
Sorcin, also termed 22 kDa Ca2+-binding protein, CP-22, or V19, is a soluble resistance-related calcium-binding protein that is expressed in normal mammalian tissues, such as the liver, lungs and heart. The up-regulation of sorcin is correlated with a number of cancer types, including colorectal, gastric and breast cancer. It may represent a therapeutic target for reversing tumor multidrug resistance (MDR). Sorcin participates in the regulation of calcium homeostasis in cells and is necessary for the activation of mitosis and cytokinesis. It enhances metastasis and promotes epithelial-to-mesenchymal transition of colorectal cancer. Moreover, sorcin has been implicated in the regulation of intracellular Ca2+ cycling and cardiac excitation-contraction coupling. It displays the anti-apoptotic properties via the modulation of mitochondrial Ca2+ handling in cardiac myocytes. It can target and activate the sarcolemmal Na+/Ca2+ exchanger (NCX1) in cardiac muscle. Meanwhile, sorcin modulates cardiac L-type Ca2+ current by functional interaction with the alpha1C subunit. It also associates with calcium/calmodulin-dependent protein kinase IIdeltaC (CaMKIIdelta(C)) and further modulates ryanodine receptor (RyR) function in cardiac myocytes. Furthermore, sorcin may act as a Ca2+ sensor for glucose-induced nuclear translocation and the activation of carbohydrate-responsive element-binding protein (ChREBP)-dependent genes. As a mitochondrial chaperone TRAP1 interactor, sorcin involves in mitochondrial metabolism through the TRAP1 pathway. In addition, sorcin may regulate the inhibition of type I interferon response in cells through interacting with foot-and-mouth disease virus (FMDV) VP1. Sorcin contains a flexible glycine and proline-rich N-terminal extension and five EF-hand motifs that associate with membranes in a calcium-dependent manner. It may harbor three potential Ca2+ binding sites through its EF1, EF2 and EF3 hands. However, binding of only two Ca2+/monomer suffices to trigger the conformational change that exposes hydrophobic regions and leads to interaction with the respective targets. Sorcin forms homodimers through the association of the unpaired EF5 hand. Among the PEF proteins, sorcin is unique in that it contains potential phosphorylation sites by cAMP-dependent protein kinase (PKA), and it can form a tetramer at slightly acid pH values although remaining a stable dimer at neutral pH.
Feature 1:putative Ca binding site [ion binding site]
Evidence:
Comment:Homo sapiens sorcin may harbor three potential Ca2+ binding sites. However, binding of only two Ca2+/monomer suffices to trigger the conformational change that exposes hydrophobic regions and leads to interaction with the respective targets.
Jiyao W et al.(2023). "The conserved domain database in 2023.",