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G-Protein Coupled Receptors

G-protein coupled receptors(GCPRs) are a large family of cell surface membrane proteins. Once bound to a wide variety of extracellular ligands, GCPRs undergo a conformational change and relay information to intracellular secondary messengers ^[1]. This G protein activation results in a cellular response dependent on the ligand bound and location of the GPCR in the body. GCPRs can be broken down into five families: the rhodopsin family (class A, 701 members), the secretin family (class B, 15 members), the adhesion family (24 members), the glutamate family (class C, 15 members), and the frizzled/taste family (class F, 24 members) ^[2]. All of the families have a similar transmembrane (TM) domain consisting of seven ɑ-helices complexed with intracellular G proteins.

Class A GCPRs

Class A GPCRS or rhodopsin-like GPCRS are the largest and most studied type of GPCRS. Due to the diversity of these receptors they are found in many aspects of physiology. They are characterized by conserved motifs including DRY, PIF, Sodium Binding, and the CWxP.6 A common example of a class A GPCRS is the β2AR receptor (PDB: 3sn6).

MRGPRs

Structure with Structure with

The human itch GPCR, or Mas-related G-protein coupled receptor (MRGPR), is a Class A GPCR found in human sensory neurons and is responsible for the sensation of “itching” caused by skin irritation and diseases, insect bites, and hypersensitivity to certain drugs. There are currently four groups consisting of MRGPRX1, MRGPRX2, MRGPRX3, and MRGPRX4. In particular, MRGPRX4 is responsible for cholestatic itch while MRGPRX2 regulates degranulation and hypersensitivity itch reactions ^[3]. These two, chiefly MRGPRX2, are often targets for drugs that result in mast cell degranulation and hypersensitivity side effects. In comparison to other Class A GPCRs, MRGPRX2 binds to an even wider range of ligands, including agonists such as cations and peptides.

Cation

(R)-ZINC-3573 is a cation ligand that binds to MRGPRX2. Its N-dimethyl is inserted into a cavity of aromatic amino acid residues Phe-170, Trp-243, and Phe-244. In this cavity, it makes ion pairs with Asp-184 and Glu-164. It is then stabilized by stacking its ring with Trp-248 and the Cys-168 to Cys-180 disulfide bond ^[4].

Peptide

Specific Traits

Disulfide bonds

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PIF Motif

DRY Motif

Sodium Binding

MRGPRX2 Signaling Pathway

Function

Conformational Changes

What It Triggers

Clinical Relevance

Drugs

References

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