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A new approach to producing functional G alpha subunits yields the activated and deactivated structures of G

Barry Kreutz1, Douglas M Yau, Mark R Nance

  • 1Department of Pharmacology, University of Illinois College of Medicine, Chicago, Illinois 60612, USA.

Biochemistry
|January 4, 2006
PubMed

Insights

Researchers developed soluble chimeric G alpha(i/12) and G alpha(i/13) proteins, enabling structural studies of oncogenic G(12/13) proteins. These novel structures reveal key features for protein interactions and signaling.

Area of Science:

  • Molecular Biology
  • Structural Biology
  • Cell Signaling

Background:

  • The G(12/13) subfamily of heterotrimeric G proteins are crucial in signal transduction pathways regulating cellular processes.
  • Previous structural studies of G alpha(12/13) subunits were limited by difficulties in obtaining sufficient homogeneous, functional protein.
  • Understanding the structure of G alpha(12/13) is vital for elucidating their roles in oncogenesis and downstream signaling.

Purpose of the Study:

  • To overcome challenges in producing sufficient quantities of functional G alpha(12/13) subunits for structural analysis.
  • To determine the crystal structures of G alpha(i/12) and G alpha(i/13) chimeric proteins.
  • To investigate the structural basis for G(12/13) protein interactions with guanine nucleotides, G betagamma subunits, and effector proteins.

Main Methods:

  • Generation of soluble chimeric G alpha subunits (G alpha(i/12) and G alpha(i/13)) by substituting the N-terminal helix of G alpha(i1) with regions from G alpha12 or G alpha13.
  • Purification of chimeric subunits to homogeneity for crystallographic studies.
  • X-ray crystallography to determine the structures of G alpha(i/12) x GDP x AlF4(-) and G alpha(i/13) x GDP complexes.

Main Results:

  • Soluble and functional chimeric G alpha(i/12) and G alpha(i/13) proteins were successfully generated and purified.
  • These chimeras bound guanine nucleotides, G betagamma subunits, and effector proteins, and responded to GAP stimulation.
  • Crystal structures revealed native structural features of G alpha12 and G alpha13, including novel conformational changes linked to GTP hydrolysis.

Conclusions:

  • The developed chimeric G alpha subunits provide a platform for structural studies of the G(12/13) protein family.
  • The determined structures offer insights into the interactions of G alpha(12/13) with GPCRs and RhoGEF effectors.
  • Novel conformational changes observed are likely critical for GTP hydrolysis and signal termination in the G(12/13) pathway.

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