5kdl
Crystal structure of the 4 alanine insertion variant of the Gi alpha1 subunit bound to GTPgammaS
Structural highlights
FunctionGNAI1_RAT Guanine nucleotide-binding proteins (G proteins) are involved as modulators or transducers in various transmembrane signaling systems. The G(i) proteins are involved in hormonal regulation of adenylate cyclase: they inhibit the cyclase in response to beta-adrenergic stimuli. The inactive GDP-bound form prevents the association of RGS14 with centrosomes and is required for the translocation of RGS14 from the cytoplasm to the plasma membrane. May play a role in cell division.[1] Publication Abstract from PubMedG protein coupled receptor (GPCR) mediated heterotrimeric G protein activation is a major mode of signal transduction in the cell. Previously, we and other groups reported that the alpha 5 (alpha5) helix of Galphai1, especially the hydrophobic interactions in this region, plays a key role during nucleotide release and G protein activation. To further investigate the effect of this hydrophobic core, we disrupted it in Galphai1 by inserting 4 alanine amino acids into the alpha5 helix between residues Q333 and F334 (Ins4A). This extends the length of the alpha5 helix without disturbing the beta6-alpha5 loop interactions. This mutant has high basal nucleotide exchange activity, yet no receptor-mediated activation of nucleotide exchange. By using structural approaches, we show that this mutant loses critical hydrophobic interactions leading to significant rearrangements of side chain residues H57, F189, F191, and F336; it also disturbs the rotation of the alpha5 helix, and the pi-pi interaction between H57 and F189. In addition, the insertion mutant abolishes G protein release from the activated receptor after nucleotide binding. Our biochemical and computational data indicate that the interactions between alpha5, alpha1 and beta2-beta3 are not only vital for GDP release during G protein activation, but they are also necessary for proper GTP binding (or GDP re-binding). Thus, our studies suggest that this hydrophobic interface is critical for accurate rearrangement of the alpha5 helix for G protein release from the receptor after GTP binding. A conserved hydrophobic core in Galphai1 regulates G protein activation and release from activated receptor.,Kaya AI, Lokits AD, Gilbert JA, Iverson TM, Meiler J, Hamm HE J Biol Chem. 2016 Jul 26. pii: jbc.M116.745513. PMID:27462082[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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