Structure-based analysis of GPCR function: evidence for a novel pentameric assembly between the dimeric leukotriene B4 receptor BLT1 and the G-protein.
We produced human leukotriene B(4) (LTB(4)) receptor BLT1 as a recombinant protein in Escherichia coli. This detergent-solubilized receptor displays two states with regard to its affinity for LTB(4): (i) a low-affinity state (K(a)=7.8x10(8)M(-1)) that involves a receptor homodimer (BLT1.LTB(4))(2); we report evidence for a central role of the sixth transmembrane ... helix in regulating the stability of this homodimer; (ii) a high-affinity state (K(a)=1.3x10(10)M(-1)) upon interaction of the receptor with the heterotrimeric GDP-loaded G-protein, Galpha(i2)beta(1)gamma(2). Association of the G-protein with recombinant BLT1 induces GDP-GTP exchange by the Galpha subunit. These results indicate that isolated BLT1 is fully representative of the in vivo receptor with regard to high-affinity recognition of LTB(4), association with a G-protein and activation of Galpha. Using a combination of mass spectrometry after chemical cross-linking and neutron-scattering in solution with the native complex, we establish unambiguously that only one G-protein trimer binds to a receptor dimer to form the stoichiometrically defined (BLT1.LTB(4))(2):Galpha(i2)beta(1)gamma(2) pentameric assembly. This suggests that receptor dimerization could be crucial to transduction of the LTB(4)-induced signal.
Mesh Terms:
Circular Dichroism, Cross-Linking Reagents, Cysteine, Dimerization, Escherichia coli, Fluorescence, GTP-Binding Protein alpha Subunits, Gi-Go, GTP-Binding Proteins, Guanosine Diphosphate, Guanosine Triphosphate, Heterotrimeric GTP-Binding Proteins, Humans, Leukotriene B4, Ligands, Models, Molecular, Neutrons, Protein Conformation, Receptors, Leukotriene B4, Recombinant Proteins, Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization, Structure-Activity Relationship
Circular Dichroism, Cross-Linking Reagents, Cysteine, Dimerization, Escherichia coli, Fluorescence, GTP-Binding Protein alpha Subunits, Gi-Go, GTP-Binding Proteins, Guanosine Diphosphate, Guanosine Triphosphate, Heterotrimeric GTP-Binding Proteins, Humans, Leukotriene B4, Ligands, Models, Molecular, Neutrons, Protein Conformation, Receptors, Leukotriene B4, Recombinant Proteins, Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization, Structure-Activity Relationship
J. Mol. Biol.
Date: Jun. 13, 2003
PubMed ID: 12787680
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