Parvalbumin
Calcium-binding protein with low molecular weight From Wikipedia, the free encyclopedia
Calcium-binding protein with low molecular weight From Wikipedia, the free encyclopedia
Parvalbumin (PV) is a calcium-binding protein with low molecular weight (typically 9-11 kDa). In humans, it is encoded by the PVALB gene. It is a member of the albumin family; it is named for its size (parv-, from Latin parvus which means "small") and its ability to coagulate.
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Aliases | PVALB, D22S749, parvalbumin | ||||||||||||||||||||||||||||||||||||||||||||||||||
External IDs | OMIM: 168890; MGI: 97821; HomoloGene: 2137; GeneCards: PVALB; OMA:PVALB - orthologs | ||||||||||||||||||||||||||||||||||||||||||||||||||
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It has three EF hand motifs and is structurally related to calmodulin and troponin C. Parvalbumin is found in fast-contracting muscles, where its levels are highest, as well as in the brain and some endocrine tissues.
Parvalbumin is a small, stable protein containing EF-hand type calcium binding sites. It is involved in calcium signaling. Typically, this protein is broken into three domains, domains AB, CD and EF, each individually containing a helix-loop-helix motif.[5] The AB domain houses a two amino-acid deletion in the loop region, whereas domains CD and EF contain the N-terminal and C-terminal, respectively.[5]
Calcium binding proteins like parvalbumin play a role in many physiological processes, namely cell-cycle regulation, second messenger production, muscle contraction, organization of microtubules and phototransduction.[6] Therefore, calcium-binding proteins must distinguish calcium in the presence of high concentrations of other metal ions. The mechanism for the calcium selectivity has been extensively studied.[6][7]
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Parvalbumin is present in some GABAergic interneurons in the nervous system, especially the reticular thalamus,[8] and expressed predominantly by chandelier and basket cells in the cortex. In the cerebellum, PV is expressed in Purkinje cells and molecular layer interneurons.[9] In the hippocampus, PV+ interneurons are subdivided into basket, axo-axonic, and bistratified cells, each subtype targeting distinct compartments of pyramidal cells.[10]
PV interneurons' connections are mostly perisomatic (around the cell body of neurons). Most of the PV interneurons are fast-spiking. They are also thought to give rise to gamma waves recorded in EEG.
PV-expressing interneurons represent approximately 25% of GABAergic cells in the primate DLPFC.[11][12] Other calcium-binding protein markers are calretinin (most abundant subtype in DLPFC, about 50%) and calbindin. Interneurons are also divided into subgroups by the expression of neuropeptides such as somatostatin, neuropeptide Y, cholecystokinin.
PV is known to be involved in relaxation of fast-twitch muscle fibers.[13][14] This function is associated with PV role in calcium sequestration.
During muscle contraction, the action potential stimulate voltage-sensitive proteins in T-tubules membrane. These proteins stimulate the opening of Ca2+ channels in the sarcoplasmic reticulum, leading to release of Ca2+ in the sarcoplasm. The Ca2+ ions bind to troponin, which causes the displacement of tropomyosin, a protein that prevents myosin walking along actin. The displacement of tropomyosin exposes the myosin-binding sites on actin, permitting muscle contraction.[15]
This way, while muscle contraction is driven by Ca2+ release, muscle relaxation is driven by Ca2+ removal from sarcoplasm. Along with Ca2+ pumps, PV contributes to Ca2+ removal from cytoplasm: PV binds to Ca2+ ions in the sarcoplasm, and then shuttles it to the sarcoplasmic reticulum.[16]
Decreased PV and GAD67 expression was found in PV+ GABAergic interneurons in schizophrenia.[17][18]
Parvalbumin has been identified as an allergen causing fish allergy (but not shellfish allergy).[19][20][21][22] Bony fishes manifest β-parvalbumin and cartilaginous fishes such as sharks and rays manifest α-parvalbumin; allergenicity to bony fishes has a low cross-reactivity to cartilaginous fishes.[20]
The protein was discovered in 1965 as a component of the fast-twitching white muscle of fish. It was described as a low molecular-weight "albumin".[23] It is unknown who coined the term parvalbumin, but the word is already in use by 1967.[24]
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