Details

Autor(en) / Beteiligte

• Scheerer, Patrick
• Heck, Martin
• Goede, Andrean
• Park, Jung Hee
• Choe, Hui-Woog
• Ernst, Oliver P.
• Hofmann, Klaus Peter
• Hildebrand, Peter W.
• Hubbell, Wayne L.

Titel

Structural and Kinetic Modeling of an Activating Helix Switch in the Rhodopsin-Transducin Interface

Ist Teil von

• Proceedings of the National Academy of Sciences - PNAS, 2009-06, Vol.106 (26), p.10660-10665

Ort / Verlag

United States: National Academy of Sciences

Erscheinungsjahr

2009

Link zum Volltext

Quelle

MEDLINE

Beschreibungen/Notizen

• Extracellular signals prompt G protein-coupled receptors (GPCRs) to adopt an active conformation (R*) and catalyze GDP/GTP exchange in the α-subunit of intracellular G proteins (Gαβγ). Kinetic analysis of transducin $(G_t \alpha \beta \gamma )$ activation shows that an intermediary ${\rm{R*G}}_{\rm{t}} \alpha \beta \gamma {\rm{ - GDP}}$ complex is formed that precedes GDP release and formation of the nucleotide-free R*·G protein complex. Based on this reaction sequence, we explore the dynamic interface between the proteins during formation of these complexes. We start from the R* conformation stabilized by a ${\rm{G}}_{\rm{t}} \alpha $ C-terminal peptide (GαCT) obtained from crystal structures of the GPCR opsin. Molecular modeling allows reconstruction of the fully elongated C-terminal α-helix of ${\rm{G}}_{\rm{t}} \alpha $ (α5) and shows how α5 can be docked to the open binding site of R*. Two modes of interaction are found. One of them – termed stable or S-interaction – matches the position of the GαCT peptide in the crystal structure and reproduces the hydrogen-bonding networks between the C-terminal reverse turn of GαCT and conserved E(D) RY and ${\rm{NPxxY(x)}}_{5,6} {\rm{F}}$ regions of the GPCR. The alternative fit – termed intermediary or I-interaction – is distinguished by a tilt (42°) and rotation (90°) of α5 relative to the S-interaction and shows different α5 contacts with the ${\rm{NPxxY(x)}}_{5,6} {\rm{F}}$ region and the second cytoplasmic loop of R*. From the 2 α5 interactions, we derive a "helix switch" mechanism for the transition of ${\rm{R*G}}_{\rm{t}} \alpha \beta \gamma {\rm{ - GDP}}$ to the nucleotide-free R*·G protein complex that illustrates how α5 might act as a transmission rod to propagate the conformational change from the receptor-G protein interface to the nucleotide binding site.