Neurophysin II is a

carrier protein A membrane transport protein (or simply transporter) is a membrane protein involved in the movement of ions, small molecules, and macromolecules, such as another protein, across a biological membrane. Transport proteins are integral transmembrane ...

with a size of 19,687.3 Da and is made up of a

dimer Dimer may refer to: * Dimer (chemistry), a chemical structure formed from two similar sub-units ** Protein dimer, a protein quaternary structure ** d-dimer * Dimer model, an item in statistical mechanics, based on ''domino tiling'' * Julius Dimer ( ...

of two virtually identical chains of

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...

s. Neurophysin II is a cleavage product (formed by splitting of a compound molecule into a simpler one) of the

AVP gene Arginine Vasopressin (AVP) Gene is a gene whose product is proteolytically cleaved to produce vasopressin (also known as antidiuretic hormone (ADH)), neurophysin II, and a glycoprotein called copeptin. AVP and other AVP-like peptides are found ...

. It is a neurohypophysial

hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...

that is transported in vesicles with

vasopressin Human vasopressin, also called antidiuretic hormone (ADH), arginine vasopressin (AVP) or argipressin, is a hormone synthesized from the AVP gene as a peptide prohormone in neurons in the hypothalamus, and is converted to AVP. It then ...

, the other cleavage product, along

axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action ...

s, from magnocellular neurons of the

hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamus ...

to the posterior lobe of the

pituitary In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland, about the size of a chickpea and weighing, on average, in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The hyp ...

. Although it is stored in neurosecretory granules with vasopressin and released with vasopressin into the bloodstream, its biological action is unclear. Neurophysin II is also known as a stimulator of

prolactin Prolactin (PRL), also known as lactotropin, is a protein best known for its role in enabling mammals to produce milk. It is influential in over 300 separate processes in various vertebrates, including humans. Prolactin is secreted from the pit ...

secretion.

Function

Neurophysin II is a carrier protein for vasopressin (ADH). It is produced in the cell bodies of the paraventricular and supraoptic nuclei and transported to its site of release in the axon terminals of the posterior pituitary.

Oxytocin Oxytocin (Oxt or OT) is a peptide hormone and neuropeptide normally produced in the hypothalamus and released by the posterior pituitary. It plays a role in social bonding, reproduction, childbirth, and the period after childbirth. Oxytoci ...

, a hormone similar in structure to vasopressin, is analogously bound and transported by Neurophysin I. Both hormones are nine residues long, and only differ by the amino acids at positions three and eight. Oxytocin possesses Ile-3 whereas vasopressin possesses Phe-3. Both Ile and Phe are hydrophobic amino acids and undergo analogous binding to neurophysins.

Structure

Neurophysin II is a dimer with each monomer consisting of two anti-parallel β-sheets. Each chain is identical with the exception of a single amino acid substitution (Chain 1 contains Lys-18, whereas chain 2 contains Ala-18). Each chain is 95 amino acids in length and binds a single oxytocin molecule. The amino acid sequence of Neurophysin II is: NH₂ - Ala - Met - Ser - Asp - Leu - Glu - Leu - Arg - Gln - Cys - Leu - Pro - Cys - Gly - Pro - Gly - Gly - Lys - Gly - Arg - Cys - Phe - Gly - Pro - Ser - Ile - Cys - Cys - Ala - Asp - Glu - Leu - Gly - Cys - Phe - Val - Gly - Thr - Ala - Glu - Ala - Leu - Arg - Cys - Gln - Glu - Glu - Asn - Tyr - Leu - Pro - Ser - Pro - Cys - Gln - Ser - Gly - Gln - Lys - Ala - Cys - Gly - Ser - Gly - Gly - Arg - Cys - Ala - Ala - Phe - Gly - Val - Cys - Cys - Asn - Asp - Glu - Ser - Cys - Val - Thr - Glu - Pro - Glu - Cys - Arg - Glu - Gly - Phe - His - Arg - Arg - Ala - OH (Disulfide - bridge: - 10-54; - 13-27; - 21-44; - 28-34; - 61-73; - 67-85; - 74-79)

Clinical significance

Point mutations in the genes that encode arginine vasopressin and or its carrier protein neurophysin II underlie most cases of the familial, autosomal dominant disorder neurohypophyseal diabetes insipidus. (also called hereditary hypothalamic

diabetes insipidus Diabetes insipidus (DI), recently renamed to Arginine Vasopressin Deficiency (AVP-D) and Arginine Vasopressin Resistance (AVP-R), is a condition characterized by large amounts of dilute urine and increased thirst. The amount of urine produced ...

). This condition results from insufficient ADH release into systemic circulation.

References

External links

* {{Oxytocin and vasopressin receptor modulators

Function

Structure

Clinical significance

See also

References

External links