Structure, Function, and Dynamics of the Gα Binding Domain of Ric-8A.

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Ric-8A functions as a molecular chaperone and guanine nucleotide exchange factor (GEF).
• It regulates heterotrimeric G protein alpha subunits (Gα) of the i, q, and 12/13 classes.
• Understanding Ric-8A's structure is key to deciphering G protein signaling pathways.

Purpose of the Study:

• To determine the 2.2-Å crystal structure of the Ric-8A Gα-binding domain (residues 1-452).
• To investigate the impact of phosphorylation on Ric-8A structure and Gα binding.
• To elucidate the mechanism of GEF activity in G protein regulation.

Main Methods:

• X-ray crystallography to obtain high-resolution structure of Ric-8A Gα-binding domain.
• Small-angle X-ray scattering (SAXS) with normal mode modeling to analyze structural dynamics.
• Nuclear Magnetic Resonance (NMR) spectroscopy (2D 1H-15N-TROSY) to study Gαi1 interactions.

Main Results:

• The structure reveals a superhelical fold (residues 1-429) with Armadillo (ARM) and HEAT repeats; the C terminus is disordered.
• Phosphorylation sites (Ser435, Thr440) were identified, with one potentially interacting with a basic ARM cluster.
• SAXS data suggests phosphorylation induces domain rotation, and NMR shows altered Gαi1 nucleotide binding residues upon interaction with Ric-8A R452.

Conclusions:

• The Ric-8A Gα-binding domain structure provides insights into its GEF mechanism.
• Phosphorylation plays a regulatory role in Ric-8A's conformational dynamics and Gα interaction.
• These findings contribute to understanding the regulation of G protein signaling pathways.