Granin (chromogranin and secretogranin) is a
protein family of regulated secretory
proteins ubiquitously found in the cores of amine and peptide
hormone and neurotransmitter dense-core secretory vesicles.[2]
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 vitro 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.
Structure
Apart from their subcellular location and the abundance of acidic residues (
Asp 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.
There are considerable differences in the amino acid composition between different animals. Commercial assays for measuring human CGA can usually not be used for measuring CGA in samples from other species. Some specific parts of the molecule have a higher degree of amino acid homology and methods where the antibodies are directed against specific epitopes can be used to measure samples from different animals.[3] Region-specific assays measuring defined parts of CGA, CGB and SG2 can be used for measurements in samples from cats and dogs.[4][5][6][7]
Some other proteins are also proposed to belong to the granins based on their physico-chemical properties. These include
NESP55 (SgVI),
VGF (SgVII), and
ProSAAS (SgVIII).[8]
References
^Preece NE, Nguyen M, Mahata M, Mahata SK, Mahapatra NR, Tsigelny I, O'Connor DT (April 2004). "Conformational preferences and activities of peptides from the catecholamine release-inhibitory (catestatin) region of chromogranin A". Regulatory Peptides. 118 (1–2): 75–87.
doi:
10.1016/j.regpep.2003.10.035.
PMID14759560.
S2CID43517955.
^Huttner WB, Gerdes HH, Rosa P (January 1991). "The granin (chromogranin/secretogranin) family". Trends in Biochemical Sciences. 16 (1): 27–30.
doi:
10.1016/0968-0004(91)90012-K.
PMID2053134.
