# Granin

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.

## 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 Ca$^{2+}$, 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. Region-specific assays measuring defined parts of CGA, CGB and SG2 can be used for measurements in samples from cats and dogs.

## Members
### Chromogranins

* chromogranin A (CgA)
* chromogranin B (CgB)
| chromogranin A (parathyroid secretory protein 1)IdentifiersSymbolCHGAAlt. symbolsCGANCBI gene1113HGNC1929OMIM118910RefSeqNM_001275UniProtP10645Other dataLocusChr. 14 q32Search forStructuresSwiss-modelDomainsInterPro | chromogranin B (secretogranin 1)IdentifiersSymbolCHGBAlt. symbolsSCG1NCBI gene1114HGNC1930OMIM118920RefSeqNM_001819UniProtP05060Other dataLocusChr. 20 pter-p12Search forStructuresSwiss-modelDomainsInterPro |

### Secretogranins

* secretogranin II (SgII) (see also secretoneurin)
* secretogranin III (SgIII)
* secretogranin V (SgV)
| secretogranin II (chromogranin C)IdentifiersSymbolSCG2Alt. symbolsCHGC, SgIINCBI gene7857HGNC10575OMIM118930RefSeqNM_003469UniProtP13521Other dataLocusChr. 2 q35-q36Search forStructuresSwiss-modelDomainsInterPro | secretogranin III (FLJ90833)IdentifiersSymbolSCG3Alt. symbolsSGIIINCBI gene29106HGNC13707OMIM611796RefSeqNM_013243UniProtQ8WXD2Other dataLocusChr. 15 q21.3Search forStructuresSwiss-modelDomainsInterPro | secretogranin V (7B2 protein)IdentifiersSymbolSCG5Alt. symbolsSGNE1NCBI gene6447HGNC10816OMIM173120RefSeqNM_003020UniProtP05408Other dataLocusChr. 15 q13-q14Search forStructuresSwiss-modelDomainsInterPro |

### Extended group

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).