Synthesis and Variants
The mRNA from the ghrl gene codes for a 117 amino acid peptide called preproghrelin, containing 4 exons of the GHRL gene. The signalling peptide molecule of this larger precursor is cleaved to produce proghrelin. Proghrelin is cleaved in two to produce the 28 amino acid peptide ghrelin (unacylated) and C-ghrelin (of which obestatin is presumed to be a cleaved form).
'Ghrelin' usually refers to the octanoylated form of ghrelin (acyl ghrelin). This is the 28 amino acid peptide sequence with an octanoylation on the third amino acid (Serine). The octanoylation is performed by the Ghrelin O-acyltransferase (GOAT) protein (a member of the membrane-bound O-Acyltransferase family of proteins), located in the stomach and pancreas. This peptide can activate the GHSR receptor and is thus known as the active form of ghrelin. The non-octanoylated form is known as desacyl ghrelin or the inactive form (it does not activate GHSR1a and thus does not release GH like acyl ghrelin), however studies have shown it has its own effects. Side chains other than octanoyl have also been observed.
Read more about this topic: Ghrelin
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