Neurophysins are carrier proteins which transport the

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 ...

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, ...

and

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 ...

to the

posterior pituitary The posterior pituitary (or neurohypophysis) is the posterior lobe of the pituitary gland which is part of the endocrine system. Unlike the anterior pituitary, the posterior pituitary is not glandular, but largely a collection of axonal projec ...

from the paraventricular and

supraoptic nucleus The supraoptic nucleus (SON) is a nucleus of magnocellular neurosecretory cells in the hypothalamus of the mammalian brain. The nucleus is situated at the base of the brain, adjacent to the optic chiasm. In humans, the SON contains about 3,000 ...

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 ...

, respectively. Inside the neurosecretory granules, the analogous neurophysin I and II form stabilizing complexes via

covalent A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atom ...

interactions. Stabilizing neurophysin-hormone complexes that are formed within neurosecretory granules located in the posterior pituitary gland aid in intra-axonal transport. During intra-axonal transport, the neurophysin's are believed to prevent the bound hormone from leaking into the cytoplasmic space and proteolytic digestion via enzymes. However, due to the low concentration of neurophysin in the blood, it is likely the protein-hormone complex dissociates, indicating the neurophysin does not aid in transporting the hormone through the

circulatory system In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. It includes the cardiovascular system, or vascular system, that consists of the heart ...

. Neurophysins are also secreted out of the posterior pituitary hypothalamus, each carrying their respective associated passenger hormone. When the posterior pituitary hypothalamus secretes vasopressin and its neurophysin carrier, it also secretes a glycopeptide. There are two types: *

Neurophysin I Neurophysin I is a carrier protein with a size of 10 K Da and contains 90 to 97 amino acids. It is a cleavage product (formed by splitting of a compound molecule into a simpler one) of preprooxyphysin. It is a neurohypophysial hormone that is tra ...

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, ...

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

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 ...

(Also known as "antidiuretic hormone" or ADH)

Biosynthesis of Neurophysins

These proteins are synthesized in the cell bodies of the supraoptic and paraventricular regions of the

. The

disulfide In chemistry, a disulfide (or disulphide in British English) is a compound containing a functional group or the anion. The linkage is also called an SS-bond or sometimes a disulfide bridge and usually derived from two thiol groups. In inorg ...

-rich neurophysin protein is suggested to be congruent with the synthesis of

insulin Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the insulin (''INS)'' gene. It is the main Anabolism, anabolic hormone of the body. It regulates the metabol ...

in which a precursor molecule of higher molecular weight is proteolytically cleaved and forms disulfide linkages. Although not enough data has been obtained, it is hypothesized that there is a common precursor molecule between neurophysin and the two hormones it stabilizes.

Structure

Neurophysins are acidic proteins with a molecular weight of approximately 10,000 Da that are rich in

cysteine Cysteine (; symbol Cys or C) is a semiessential proteinogenic amino acid with the chemical formula, formula . The thiol side chain in cysteine enables the formation of Disulfide, disulfide bonds, and often participates in enzymatic reactions as ...

glycine Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid. Glycine is one of the proteinogenic amino acids. It is encoded by all the codons starting with GG (G ...

, and

proline Proline (symbol Pro or P) is an organic acid classed as a proteinogenic amino acid (used in the biosynthesis of proteins), although it does not contain the amino group but is rather a secondary amine. The secondary amine nitrogen is in the p ...

residues . The protein is double domain with a

polypeptide chain Peptides are short chains of amino acids linked by peptide bonds. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides that have a molecular mass of 10,000 Da or more are called proteins. Chains of fewer than twenty ami ...

of 93-95 residues with 14 cysteine residues forming 7 disulfide bridges . Domain I contains a COOH terminal with a disulfide loop; domain II lacks this COOH terminal disulfide loop . Based on the resemblance of the disulfide loop present on vasopressin and oxytocin, it is suggested that the hormones form covalent linkages to this disulfide loop present on the COOH terminal of domain I. PDB 1npo EBI

References

External links

* Membrane biology Biological matter {{biochemistry-stub

Biosynthesis of Neurophysins

Structure

See also

References

External links