Chromogranin
Encyclopedia
Granin is a protein family
of regulated secretory protein
s ubiquitously found in the cores of amine and peptide hormone
and neurotransmitter dense-core secretory vesicles.
and in vivo
. The intracellular biochemistry of granins includes binding of Ca2+, ATP and catecholamines (epinephrine
, norepinephrine
) within the hormone storage vesicle core. There is also evidence that CgA, and perhaps other granins, regulate the biogenesis of dense-core secretory vesicles and hormone sequestration in neuroendocrine cells.
and Glu
), these proteins do not share many structural similarities. Only one short region, located in the C-terminal section, is conserved in all these proteins. Chromogranins and secretogranins together share a C-terminal motif, whereas chromogranins A and B share a region of high similarity in their N-terminal section; this region includes two cysteine
residues involved in a disulfide bond
.
Two other proteins (secretogranin IV and VI) are also proposed to belong to the granins on the basis of their physico-chemical properties.
Protein family
A protein family is a group of evolutionarily-related proteins, and is often nearly synonymous with gene family. The term protein family should not be confused with family as it is used in taxonomy....
of regulated secretory protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s ubiquitously found in the cores of amine and peptide hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
and neurotransmitter dense-core secretory vesicles.
Function
Granins (chromogranins or secretogranins) are acidic proteins and are present in the secretory granules of a wide variety of endocrine and neuro-endocrine cells. The exact function(s) of these proteins is not yet settled but there is evidence that granins function as pro-hormones, giving rise to an array of peptide fragments for which autocrine, paracrine, and endocrine activities have been demonstrated in vitroIn vitro
In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...
and in vivo
In vivo
In vivo is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research...
. The intracellular biochemistry of granins includes binding of Ca2+, ATP and catecholamines (epinephrine
Epinephrine
Epinephrine is a hormone and a neurotransmitter. It increases heart rate, constricts blood vessels, dilates air passages and participates in the fight-or-flight response of the sympathetic nervous system. In chemical terms, adrenaline is one of a group of monoamines called the catecholamines...
, norepinephrine
Norepinephrine
Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter...
) within the hormone storage vesicle core. There is also evidence that CgA, and perhaps other granins, regulate the biogenesis of dense-core secretory vesicles and hormone sequestration in neuroendocrine cells.
Structure
Apart from their subcellular location and the abundance of acidic residues (AspAspartic acid
Aspartic acid is an α-amino acid with the chemical formula HOOCCHCH2COOH. The carboxylate anion, salt, or ester of aspartic acid is known as aspartate. The L-isomer of aspartate is one of the 20 proteinogenic amino acids, i.e., the building blocks of proteins...
and Glu
Glutamic acid
Glutamic acid is one of the 20 proteinogenic amino acids, and its codons are GAA and GAG. It is a non-essential amino acid. The carboxylate anions and salts of glutamic acid are known as glutamates...
), these proteins do not share many structural similarities. Only one short region, located in the C-terminal section, is conserved in all these proteins. Chromogranins and secretogranins together share a C-terminal motif, whereas chromogranins A and B share a region of high similarity in their N-terminal section; this region includes two cysteine
Cysteine
Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid...
residues involved in a disulfide bond
Disulfide bond
In chemistry, a disulfide bond is a covalent bond, usually derived by the coupling of two thiol groups. The linkage is also called an SS-bond or disulfide bridge. The overall connectivity is therefore R-S-S-R. The terminology is widely used in biochemistry...
.
Chromogranins
- chromogranin AChromogranin AChromogranin A or parathyroid secretory protein 1 is a member of the granin family of neuroendocrine secretory proteins, i.e. it is located in secretory vesicles of neurons and endocrine cells...
(CgA) - chromogranin BSecretoneurinSecretoneurin, also called Chromogranin B , is a 33-amino acid neuropeptide derived from secretogranin II . Because of this secretogranin II is also called secretoneurin-included ....
(CgB)
Secretogranins
- secretogranin IISCG2SCG2, also called secretogranin II , is a protein which in humans is encoded by the SCG2 gene.- Function :The protein encoded by this gene is a member of the chromogranin/secretogranin family of neuroendocrine secretory proteins...
(SgII) (see also secretoneurinSecretoneurinSecretoneurin, also called Chromogranin B , is a 33-amino acid neuropeptide derived from secretogranin II . Because of this secretogranin II is also called secretoneurin-included ....
) - secretogranin IIISCG3Secretogranin III, also known as SCG3, is a protein which in humans is encoded by the SCG3 gene.- Function:The protein encoded by this gene is a member of the chromogranin/secretogranin family of neuroendocrine secretory proteins. Granins may serve as precursors for biologically active peptides...
(SgIII) - secretogranin VSCG5Neuroendocrine protein 7B2 is a protein that in humans is encoded by the SCG5 gene. The protein expressed by this gene is widely distributed in neuroendocrine tissues. It functions as a chaperone protein for the proprotein convertase PC2 and is required for the production of an active PC2...
(SgV)
Two other proteins (secretogranin IV and VI) are also proposed to belong to the granins on the basis of their physico-chemical properties.