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Calcium binding protein P22 is a phosphoprotein that binds to sodium hydroxide exchanger (NHEs) and Ca2+. It can act as a transporter, regulator or activator to control the concentration of Ca2+ in the cytoplasm participate in various cell functions, decode Ca2+ signals, and regulate the concentration of Ca2+ in the cell.
Figure 1. Some P22 with their Locatins & Functions (http://www. apsubiology. org).
P22 and Calcium Ions
Calcium ions act as a second messenger to control a wide range of physiological effects. Disorders of intracellular calcium levels can lead to irreversible damage and even disease. Therefore, calcium homeostasis, is very important and requires very strict regulation. In cells, the role of Ca2+ is largely dependent on large amounts of P22, which has the ability to bind to this ion in specific regions. For example, the family of vertebrate ef-hand Ca2+ binding protein S100 (soluble in saturated ammonium sulfate) affects a variety of biological processes, including cell cycle progression, cell growth, cell viability, transcription and cell differentiation.
In addition, P22 controls the concentration of Ca2+ in the cytoplasm by acting as a Ca2+ transporter on the cell membrane or a Ca2+ modulation sensor participating in multiple cell functions. For example, calsyntenin is expressed on ER/golgi bodies and plasma membranes of almost all neurons regulating post-synaptic signaling and APP lysis. In presynaptic vesicles, synaptic binding protein is a highly conserved P22 that promotes the release of neurotransmitters by triggering extracellular secretions.
The P22 contains a highly conserved helix-ring-helix structure or EF chiral sequence. In general, EF chiral motifs come in pairs (EF chiral motifs) and facilitate the synergistic binding of two Ca2+ ions in each domain. However, P22s containing single or odd number of EF chiral motifs have also been found in bacteria and eukaryotes, and are thought to play a role through the dimerization mechanism.
Some of these Ca2+ binding proteins, such as CaM, the most common Ca2+ binding proteins, exist in the cytoplasm, organelles, or cell membranes of eukaryotic cells as Ca2+ receptors. Other proteins appear to act as storage devices for Ca2+ (such as calcium-flavine, calcium web). Structurally, calmodulin is an acidic protein composed of two spherical structural domains (each region has a pair of EF hands) connected by a flexible spiral region.
Role in Disease
Of the more than 200 ef-hand calcium-binding protein family members in the human body, the most studied are calretinin (CR), calbindin d-28k (CB) and parvalbumin (PV). CR is mainly expressed in granulocytes and their parallel fibers, while PV and CB are distributed in axons, somatic cells, dendrites and spinal cord of purkinje cells. Studies have shown that antibodies to CR, CB, and PV are appropriate tools for demonstrating transient features and developmental changes in human fetal brain tissue and for detecting specific changes in pathological specimens. In late pregnancy, CB and CR were expressed in a variety of nerve cells in the subplate. The subplate is a very wide area under the cortical plate, which is a "waiting room" where different cortical affections reside before entering the cortical plate. At the 7th and 8th months, the cortex mesenchymal between CB- and PV-ir was observed in the deeper part of the cortex plate. Fetal hydrocephalus results in severe changes of CB-ir and PV-ir neurons in the lower and cortical plates: contraction of ir neurons, loss of process markers, and, in most cases, total loss of immune markers. These changes, which cannot be detected in nissl stained slices, indicate significant impairment in neural function.