Sandbox Reserved 1722: Difference between revisions

The DRY motif is a proton microswitch that is located near the G-protein binding site C-terminal  on TM3 <ref name="Schonegge"/>.  It acts as an ion lock when the GPCR is not being activated, preventing unnecessary activation of the G-proteins <ref name="Zhou"/>. This motif is conserved in typical Class A GPCRS however, in MRGPRX2 it is only partially conserved. The arginine is conserved, while the aspartate is replaced by a glutamate and the tyrosine is replaced by a cysteine (Figure 2.)<ref name="Yang"/> <ref name="Sandoval">Sandoval, A., et al. "The Molecular Switching Mechanism at the Conserved D(E)RY Motif in Class-A GPCRs." Biophysical journal, 111(1), 79-89. https://doi.org/10.1016/j.bpj.2016.06.004 </ref>. The replacement of tyrosine for cysteine results in the helices coming closer together, creating a shallower binding pocket.<ref name="Zhou"/>  

[[Image:Gq_and_Gi_snip.PNG|300px|right|thumb|'''Figure 4''': Caption.<ref name="Cao"/>]]

Once the ligand is bound, MRGPRX2 undergoes a conformational change that is transmitted through to the [https://en.wikipedia.org/wiki/G_protein#:~:text=G%20proteins%2C%20also%20known%20as,a%20cell%20to%20its%20interior. G-protein]. This conformational change is affected by the aforementioned deviances from Class A GPCRs. Rather than a large conformational change, a subtle one is induced. This will allow MRGPRX2 to interact with a G-protein. <scene name='90/904327/Gproteins/2'>G-proteins</scene> are composed of 3 subunits; α, β, and γ. When activated, the receptor acts as a Guanine nucleotide factor (GEF) which will allow the Gα subunit to have its GDP be replaced by a GTP. This will cause the Gα subunit to dissociate from the dimer Gβγ. The Gα subunit is then able to act as a secondary messenger to begin the signal transduction in the cell. MRGPRX2 interacts with two different types of G-proteins; Gi and Gq. These G-proteins are activated by similar interactions with the receptor however, they are structurally different and changes in the induced conformation are observed (Figure 4). Due to these structural differences, differences in ligand binding to MRGPRX2 bound to Gi in comparison to Gq are observed (Figure 5).