GNAI1 missense mutations associated with a neurodevelopmental syndrome modify Gα_i1 function.

Area of Science:

• Neuroscience
• Molecular Biology
• Genetics

Background:

• G protein-coupled receptors (GPCRs) are crucial for neurodevelopment.
• Gα_i1, a G protein subunit, mediates inhibitory GPCR signaling.
• Mutations in GNAI1 cause GNAI1 syndrome, a severe neurodevelopmental disorder.

Purpose of the Study:

• To investigate the functional impact of five GNAI1 missense variants associated with GNAI1 syndrome on GPCR signaling.
• To determine if these variants alter dopamine D2 receptor (D2R) activity and G protein function.

Main Methods:

• In silico modeling and genetic biobank data to predict variant pathogenicity.
• Expression of wild-type and variant Gα_i1 proteins in Xenopus laevis oocytes.
• Assays measuring dopamine potency at D2R, constitutive G protein activity, GTP-γ-S binding, and GTP hydrolysis.

Main Results:

• Four GNAI1 variants (T48K, T48I, C224Y, V332E) increased dopamine potency at D2R and constitutive G protein activity.
• The G40C variant showed no response to D2R activation.
• All variants exhibited reduced GTP-γ-S binding rates and undetectable GTP hydrolysis, except T48I.

Conclusions:

• Four GNAI1 variants confer a net gain-of-function effect on D2R signaling.
• All studied GNAI1 variants disrupt GTP exchange, providing a molecular basis for GNAI1 syndrome.
• GNAI1 mutations are important considerations in diagnosing rare neurodevelopmental disorders.