Structures of Gα Proteins in Complex with Their Chaperone Reveal Quality Control Mechanisms

• DOI: 10.1016/j.celrep.2020.02.086
• Publication Date: 2020-03-02T15:36:17Z
• Authors: Alpay Burak Seven; Daniel Hilger; Makaía M. Papaser...; Li Zhang; Qianhui Qu; Brian K. Kobilka; Gregory G. Tall; Georgios Skiniotis
• Keywords: Models, Molecular; Quality Control; Protein Folding; 0303 health sciences; QH301-705.5; Protein Stability; Models, Biological; Article; GTP-Binding Protein alpha Subunits; Protein Structure, Secondary; 03 medical and health sciences; HEK293 Cells; Guanine Nucleotide Exchange Factors; Humans; Amino Acid Sequence; Guanosine Triphosphate; Biology (General); Phosphorylation; Molecular Chaperones; Protein Binding

Many chaperones promote nascent polypeptide folding followed by substrate release through ATP-dependent conformational changes. Here we show cryoEM structures of Gα subunit folding intermediates in complex with full-length Ric-8A, a unique chaperone-client system in which substrate release is facilitated by guanine nucleotide binding to the client G protein. The structures of Ric-8A-Gαi and Ric-8A-Gαq complexes reveal that the chaperone employs its extended C-terminal region to cradle the Ras-like domain of Gα, positioning the Ras core in contact with the Ric-8A core while engaging its switch2 nucleotide binding region. The C-terminal α5 helix of Gα is held away from the Ras-like domain through Ric-8A core domain interactions, which critically depend on recognition of the Gα C terminus by the chaperone. The structures, complemented with biochemical and cellular chaperoning data, support a folding quality control mechanism that ensures proper formation of the C-terminal α5 helix before allowing GTP-gated release of Gα from Ric-8A.