Crystal structure of metarhodopsin II

Area of Science:

• Structural Biology
• Biochemistry
• Molecular Biology

Background:

• G-protein-coupled receptors (GPCRs) are crucial cell signaling proteins.
• Rhodopsin, a photoreceptor GPCR, initiates vision by coupling to transducin.
• Metarhodopsin II (Meta II) is a short-lived, active intermediate difficult to crystallize.

Purpose of the Study:

• To determine the high-resolution crystal structures of Meta II.
• To elucidate the structural basis of Meta II formation and G protein coupling.
• To provide structural models for the broader GPCR superfamily.

Main Methods:

• Crystallization of opsin soaked with all-trans-retinal to form Meta II.
• X-ray crystallography to obtain structures at 3.0 Å and 2.85 Å resolution.
• Co-crystallization of Meta II with a Gα subunit C-terminal fragment (GαCT2).

Main Results:

• Crystal structures of Meta II alone and in complex with GαCT2 were determined.
• The retinal ligand is properly linked via a Schiff base to Lys296.
• GαCT2 binds in a cytoplasmic crevice, consistent with G protein coupling.
• Retinal translocation and rotation are proposed to drive Meta II conformational changes.

Conclusions:

• The crystal structures provide unprecedented insights into the active Meta II state.
• These findings illuminate the mechanism of GPCR activation by light.
• The structures serve as valuable models for understanding signaling in the large GPCR family.