C5a receptor activation: Genetic identification of critical residues in four transmembrane helices

Thomas J. Baranski, Paul Herzmark, Olivier Lichtarge, Basil O. Gerber, Joshua Trueheart, Elaine C. Meng, Taroh Iiri, Søren P. Sheikh, Henry R. Bournet

Research output: Contribution to journalArticlepeer-review

122 Scopus citations


Hormones and sensory stimuli activate serpentine receptors, transmembrane switches that relay signals to heterotrimeric guanine nucleotide-binding proteins (G proteins). To understand the switch mechanism, we subjected 93 amino acids in transmembrane helices III, V, VI, and VII of the human chemoattractant C5a receptor to random saturation mutagenesis. A yeast selection identified 121 functioning mutant receptors, containing a total of 523 amino acid substitutions. Conserved hydrophobic residues are located on helix surfaces that face other helices in a modeled seven-helix bundle (Baldwin, J. M., Schertler, G. F., and Unger, V. M. (1997) J. Mol. Biol. 272, 144-164), whereas surfaces predicted to contact the surrounding lipid tolerate many substitutions. Our analysis identified 25 amino acid positions resistant to nonconservative substitutions. These appear to comprise two distinct components of the receptor switch, a surface at or near the extracellular membrane interface and a core cluster in the cytoplasmic half of the bundle. Twenty-one of the 121 mutant receptors exhibit constitutive activity. Amino acids substitutions in these activated receptors predominate in helices III and VI; other activating mutations truncate the receptor near the extracellular end of helix VI. These results identify key elements of a general mechanism for the serpentine receptor switch.

Original languageEnglish
Pages (from-to)15757-15765
Number of pages9
JournalJournal of Biological Chemistry
Issue number22
StatePublished - May 28 1999


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