Structural basis for the specific inhibition of heterotrimeric G _q protein by a small molecule

Abstract

Heterotrimeric GTP-binding proteins (G proteins) transmit extracellular stimuli perceived by G protein-coupled receptors (GPCRs) to intracellular signaling cascades. Hundreds of GPCRs exist in humans and are the targets of a large percentage of the pharmaceutical drugs used today. Because G proteins are regulated by GPCRs, small molecules that directly modulate G proteins have the potential to become therapeutic agents. However, strategies to develop modulators have been hampered by a lack of structural knowledge of targeting sites for specific modulator binding. Here we present the mechanism of action of the cyclic depsipeptide YM-254890, which is a recently discovered G q -selective inhibitor. YM-254890 specifically inhibits the GDP/GTP exchange reaction of α subunit of G q protein (Gα q ) by inhibiting the GDP release from Gα q . X-ray crystal structure analysis of the Gα q βγ–YM-254890 complex shows that YM-254890 binds the hydrophobic cleft between two interdomain linkers connecting the GTPase and helical domains of the Gα q . The binding stabilizes an inactive GDP-bound form through direct interactions with switch I and impairs the linker flexibility. Our studies provide a novel targeting site for the development of small molecules that selectively inhibit each Gα subunit and an insight into the molecular mechanism of G protein activation.

A G-protein Subunit-α11 Loss-of-Function Mutation, Thr54Met, Causes Familial Hypocalciuric Hypercalcemia Type 2 (FHH2)

“…17 Gα 11 three‐dimensional modeling was undertaken using the reported three‐dimensional structure of Gα q in complex with the small molecule inhibitor YM‐254890 (Protein Data Bank accession no. 3AH8) 18. The Gα q protein, which shares 90% identity at the amino acid level with Gα 11 ,11 was used because crystal structures of Gα 11 are not available.…”

Differences in intradomain and interdomain motion confer distinct activation properties to structurally similar Gα proteins

“…Although nearly identical in structure, Gα subunits in particular exhibit remarkable diversity of function (2)(3)(4)9). Recent analysis identified residues in Gα proteins that confer differences in effector interactions (19).…”

“…Gα proteins from different organisms and subclasses share nearly identical structural features (2)(3)(4). However, G proteins exhibit a large spectrum of nucleotide exchange and hydrolysis rates.…”

Structural Basis of G Protein-coupled Receptor-Gi Protein Interaction

“…High resolution x-ray structures have been obtained for multiple class A ("rhodopsin-like") GPCRs (3-6, 48 -56), various G protein heterotrimers (G␣␤␥) (26,57,58), and isolated G␣ subunits in different functional states (59 -61). Combined with biochemical and biophysical data, these structures reveal a surface on G␣ that is predicted to face the intracellular side of GPCRs.…”