Disease-associated mutations affect GPR56 protein trafficking and cell surface expression.

Area of Science:

• Neuroscience
• Genetics
• Molecular Biology

Background:

• Bilateral frontoparietal polymicrogyria (BFPP) is a congenital brain malformation characterized by abnormal cortical surface development.
• BFPP is associated with epilepsy, intellectual disability, and developmental delays.
• Mutations in the G protein-coupled receptor 56 (GPR56) gene are known to cause BFPP, but the underlying molecular mechanisms are not fully understood.

Purpose of the Study:

• To investigate the biochemical properties and protein trafficking of wild-type and mutant GPR56.
• To elucidate how specific GPR56 mutations identified in BFPP patients affect protein function and cellular localization.

Main Methods:

• Analysis of GPR56 protein modifications, including GPS domain cleavage and N-glycosylation.
• Assessment of GPR56 protein trafficking and cell surface expression using various mutant forms.
• Evaluation of the effect of pharmacological chaperones on rescuing mutant GPR56 cell surface expression.

Main Results:

• Wild-type GPR56 undergoes GPS domain cleavage and N-glycosylation, with the N-terminal fragment potentially released from the cell surface.
• Disease-associated mutations in the GPR56 N-terminal domain (R38Q, R38W, Y88C, C91S) impair intracellular trafficking and reduce cell surface expression.
• Mutations in the GPR56 GPS domain (C346S, W349S) severely inhibit protein cleavage and prevent trafficking beyond the endoplasmic reticulum.
• Pharmacological chaperones partially restored cell surface expression of some GPR56 mutants.

Conclusions:

• Specific BFPP-associated mutations in GPR56 disrupt protein trafficking to the plasma membrane.
• Impaired GPR56 trafficking is a key mechanism contributing to the pathogenesis of Bilateral Frontoparietal Polymicrogyria.
• Understanding these molecular defects provides insights into BFPP etiology and potential therapeutic strategies.