Role of Structural Dynamics at the Receptor G Protein Interface for Signal Transduction.

Alexander S Rose,Helmut Grubmüller,Klaus Peter Hofmann,Patrick Scheerer,Peter W Hildebrand,Ulrich Zachariae,Eugene A Permyakov

doi:10.1371/journal.pone.0143399

Abstract

GPCRs catalyze GDP/GTP exchange in the α-subunit of heterotrimeric G proteins (Gαßγ) through displacement of the Gα C-terminal α5 helix, which directly connects the interface of the active receptor (R*) to the nucleotide binding pocket of G. Hydrogen–deuterium exchange mass spectrometry and kinetic analysis of R* catalysed G protein activation have suggested that displacement of α5 starts from an intermediate GDP bound complex (R*•GGDP). To elucidate the structural basis of receptor-catalysed displacement of α5, we modelled the structure of R*•GGDP. A flexible docking protocol yielded an intermediate R*•GGDP complex, with a similar overall arrangement as in the X-ray structure of the nucleotide free complex (R*•Gempty), however with the α5 C-terminus (GαCT) forming different polar contacts with R*. Starting molecular dynamics simulations of GαCT bound to R* in the intermediate position, we observe a screw-like motion, which restores the specific interactions of α5 with R* in R*•Gempty. The observed rotation of α5 by 60° is in line with experimental data. Reformation of hydrogen bonds, water expulsion and formation of hydrophobic interactions are driving forces of the α5 displacement. We conclude that the identified interactions between R* and G protein define a structural framework in which the α5 displacement promotes direct transmission of the signal from R* to the GDP binding pocket.

Highlights

G protein coupled receptors (GPCRs) transmit extracellular signals into the cell through binding of heterotrimeric G proteins (Gαßγ, classified as Gi, Gt, Gs, . . .) and catalysing GDP/GTP exchange in the Gα subunit (Fig 1)
Our model suggests that the α5 displacement occurs within a fixed structural framework defined by the interactions between intracellular loop 2 (ICL2) of RÃ and structural elements of the G protein
Specific contacts are formed between the N-terminus of Gs α5 C-terminus (GsαCT) with ICL2 and ICL3 of β2ARÃ (Fig 2D)

Summary

Introduction

G protein coupled receptors (GPCRs) transmit extracellular signals into the cell through binding of heterotrimeric G proteins (Gαßγ, classified as Gi, Gt, Gs, . . .) and catalysing GDP/GTP exchange in the Gα subunit (Fig 1). G protein coupled receptors (GPCRs) transmit extracellular signals into the cell through binding of heterotrimeric G proteins . .) and catalysing GDP/GTP exchange in the Gα subunit (Fig 1). Detailed insights into the structural changes triggering GDP release were obtained from recent X-ray structures of inactive (R) and active receptor. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Objectives

Methods

Results

Discussion

Conclusion