Neurophysin II is a
carrier protein with a size of 19,687.3
Da and is made up of a
dimer of two virtually identical chains of
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...
s. Neurophysin II is a cleavage product (formed by splitting of a compound molecule into a simpler one) of the
''AVP'' gene. It is a neurohypophysial
hormone
A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sent to distant organs or tissues by complex biological processes to regulate physio ...
that is transported in vesicles with
vasopressin
Mammalian 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 ...
, the other cleavage product, along
axon
An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences) is a long, slender cellular extensions, projection of a nerve cell, or neuron, ...
s, from magnocellular neurons of the
hypothalamus
The hypothalamus (: hypothalami; ) is a small part of the vertebrate brain that contains a number of nucleus (neuroanatomy), nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrin ...
to the posterior lobe of the
pituitary. 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 and mammotropin, 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 secr ...
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 is a peptide hormone and neuropeptide normally produced in the hypothalamus and released by the posterior pituitary. Present in animals since early stages of evolution, in humans it plays roles in behavior that include Human bonding, ...
, 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:
NH
2 - 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) is a condition characterized by large amounts of dilute urine and increased thirst. The amount of urine produced can be nearly 20 liters per day. Reduction of fluid has little effect on the concentration of the urine. ...
). This condition results from insufficient
ADH release into systemic circulation.
See also
*
Copeptin
*
Neurophysins
*
Neurophysin I
References
External links
*
{{Oxytocin and vasopressin receptor modulators