Resistance to inhibitors of cholinesterase-8A (RIC8A)

Resistance to inhibitors of cholinesterase-8A (RIC8A) is a cytosolic protein acting as both a **guanine nucleotide exchange factor** and a **molecular chaperone** for specific classes of heterotrimeric G protein α-subunits (Gαi, Gαq, and Gα12/13)[1][3][4]. Unlike GPCRs, RIC8A’s guanine nucleotide exchange function occurs in the cytosol and is vital for the correct folding, biogenesis, and localization of Gα proteins to the membrane, thus ensuring their capability for signaling. RIC8A is essential for processes like asymmetric cell division, embryogenesis, and neural development due to its role in G protein signaling outside of canonical receptor mechanisms[3][2][7]. The protein has a core armadillo (ARM)/HEAT repeat structure and a flexible C-terminal region critical for both chaperone and GEF activities[1][2][4]. Disruption of RIC8A leads to profound developmental defects and affects cell polarity, cell cycle, and signal transduction. It is not a receptor or enzyme in the classical drug development sense but is conceptually a signaling cofactor and chaperone. There are currently no drugs directly targeting RIC8A, and its critical cellular roles make selective pharmacologic modulation challenging and potentially toxic[5].

Other names

Chaperone Ric-8ASynembryn-ASynembrynRIC8resistance to inhibitors of cholinesterase 8 homolog A

RIC8A acts as a guanine nucleotide exchange factor by catalyzing release of GDP from Gα-subunits, allowing GTP binding and activation[1][3][4]. Functions as a molecular chaperone, enabling correct folding, stability, and cellular localization of Gα-subunits[5][7][3][2]. This action is independent of cell-surface G protein-coupled receptors (GPCRs). Phosphorylation by Casein Kinase II stimulates both GEF and chaperone activities[3][4].