Parvalbumin

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.

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,

Location and function

In neural tissue

Parvalbumin is present in some

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.

In muscular tissue

PV is known to be involved in relaxation of

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]

Clinical significance

Decreased PV and

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]

History

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]

References