4n0e
From Proteopedia
Crystal structure of the K345L variant of the Gi alpha1 subunit bound to GDP
Structural highlights
Function[GNAI1_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 PubMedReceptor-mediated activation of the Galpha subunit of heterotrimeric G proteins requires allosteric communication between the receptor-binding and the guanine nucleotide-binding sites, which are separated by over 30 A. Structural changes in the allosteric network connecting these sites are predicted to be transient in the wild-type Galpha subunit, making studies of these connections challenging. In the current work, site-directed mutants that alter the energy barriers between the activation states are used as tools to better understand transient features of allosteric signaling in the Galpha subunit. The observed differences in relative receptor affinity for intact Galphai1 subunits versus C-terminal Galphai1 peptides harboring the K345L mutation are consistent with this mutation modulating the allosteric network in the protein subunit. Measurement of nucleotide exchange rates, affinity for meta II, and thermostability suggest that the K345L Galphai1 variant has reduced stability in both the GDP-bound and nucleotide-free states as compared to wild-type, but exhibits similar stability in the GTPgammaS-bound state. High-resolution X-ray crystal structures reveal conformational changes accompanying the destabilization of the GDP-bound state. Of these, a new conformation for Switch I was stabilized by an ionic interaction with the P-loop. Further site-directed mutagenesis suggests that this interaction between Switch I and the P-loop is important for receptor-mediated nucleotide exchange in the wild-type Galphai subunit. A Transient Interaction Between the P-loop and Switch I Contributes to the Allosteric Network Between Receptor and Nucleotide in Galphai1.,Thaker TM, Sarwar M, Preininger AM, Hamm HE, Iverson TM J Biol Chem. 2014 Mar 4. PMID:24596087[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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