A conserved phenylalanine as relay between the {alpha}5 helix and the GDP binding region of heterotrimeric Gi protein {alpha} subunit [Signal Transduction]

July 25th, 2014 by Kaya, A. I., Lokits, A. D., Gilbert, J. A., Iverson, T. M., Meiler, J., Hamm, H. E.

G protein activation by G protein coupled receptors (GPCRs) is one of the critical steps for many cellular signal transduction pathways. Previously, we and other groups reported that the alpha 5 (α5) helix in the G protein alpha subunit plays a major role during this activation process. However, the precise signaling pathway between the α5 helix and the GDP binding pocket remains elusive. Here, using structural, biochemical and computational techniques, we probed different residues around the α5 helix for their role in signaling. Our data showed that perturbing the F336 (α5) residue disturbs hydrophobic interactions with the β2-β3 strands and α1 helix, leading to high basal nucleotide exchange. However, mutations in β strands β5 and β6 do not perturb G protein activation. We have highlighted critical residues that leverage F336 as a relay. Conformational changes are transmitted starting from F336 via β2-β3/α1 to Switch I and the P-loop, decreasing the stability of the GDP binding pocket and triggering nucleotide release. When the α1 and α5 helices were cross-linked, inhibiting the receptor-mediated displacement of the C-terminal α5 helix, mutation of F336 still leads to high basal exchange. This suggests that unlike receptor mediated activation, helix 5 rotation and translocation is not necessary for GDP release from the α subunit. Rather, destabilization of the backdoor region of the Gα subunit is sufficient for triggering the activation process
  • Posted in Journal of Biological Chemistry, Publications
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