The Green Line is an auxiliary pathway to enhance glucose stimulation and secretion. This is a G-protein coupled receptor (GPCR) dependent pathway.
This is Glucagon-like peptide-1 (GLP-1).
GLP-1 is a peptide hormone released by small intestinal L-cells after sensing nutrient intake, usually after a meal. It helps enhance glucose stimulated insulin secretion (Orange Line) by acting directly on pancreatic beta cells.
This is the GLP-1 Receptor (GLP1R).
GLP1R is a GPCR naturally present on the beta cell surface.
GLP1R starts off unactivated. GLP-1 binds to the GLP-1 receptor on the surface of beta cells, which causes a conformational change of GLP1R. Now GLP1R is activated
This is the G Protein.
G proteins are signaling partners of GLP1R. Activated GLP1R can activate a G protein complex. This starts a signaling cascade.
The G protein has 3 parts (alpha, beta, and gamma). In response to receptor activation, the alpha subunit of the G protein swaps out GDP inside the protein for GTP.
This is G alpha.
Once activated, the GTP-bound subunit breaks away from the beta and gamma subunits. G alpha has many destinations, one of which is moving to the Blue Line to continue the signaling cascade.
Watch a video explaining how this G-coupled receptor works.