Insights into the structure and molecular basis of ligand docking to the G protein-coupled secretin receptor using charge-modified amino-terminal agonist probes

Maoqing Dong, Delia I. Pinon, Laurence J. Miller

Research output: Contribution to journalArticle

13 Scopus citations


The amino terminus and third loop regions of class B G protein-coupled receptors play critical roles in ligand docking and action. For the prototypic secretin receptor, the hormone amino terminus is spatially approximated with receptor region high in transmembrane segment 6 (TM6), whereas residues ranging from position 6 through 26 label the amino terminus. Here, we focus on the role of charge of the secretin amino terminus, using a series of full-agonist, acetylated probes. Sites of covalent labeling were examined using sequential purification, chemical and enzymatic cleavage, and Edman degradation. High-affinity amino-terminally-blocked probes labeled the distal amino-terminal tail, rather than TM6, while adding a basic residue, again labeled TM6. These data suggest that the secretin amino terminus docks between the amino terminus and TM6 of the receptor, with this region of secretin likely interacting with an acidic residue within the receptor TM6 and the third extracellular loop. To explore this, candidate acidic residues were mutated to Ala (E341A, D342A, E345A, E351A). The E351A mutant markedly interfered with binding, biological activity, and internalization, whereas all others bound secretin and signaled and internalized normally. This supports the possibility that there is a charge-charge interaction between this residue and the amino terminus of secretin that is critical to its normal docking.

Original languageEnglish (US)
Pages (from-to)1821-1836
Number of pages16
JournalMolecular Endocrinology
Issue number7
StatePublished - Jul 1 2005


ASJC Scopus subject areas

  • Molecular Biology
  • Endocrinology

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