Direct identification of a second distinct site of contact between cholecystokinin and its receptor

Elizabeth M. Hadac, Delia I. Pinon, Zongshi Ji, Eileen L. Holicky, Randal M. Henne, Terry P. Lybrand, Laurence J. Miller

Research output: Contribution to journalArticle

78 Scopus citations

Abstract

We have developed a biologically active analogue of cholecystokinin (CCK) that incorporates a photolabile benzoylphenylalanine (Bpa) moiety in the middle of its pharmacophoric domain, which efficiently establishes a covalent bond with an interacting domain of the CCK receptor. This probe incorporated L-Bpa in the position of Gly29 of the well characterized, radioiodinatable CCK analogue, D-Tyr-Gly-[(Nle28,31)CCK-26-33]. It was a potent pancreatic secretagogue (EC50 = 28 ± 6 nM) that was equally efficacious with natural CCK, and bound to the CCK receptor with moderate affinity (IC50 = 450 ± 126 nM). This was adequate to allow specific covalent labeling of the receptor. The labeled domain was within the cyanogen bromide fragment of the receptor including the top of TM6 (the sixth transmembrane domain), the third extracellular loop, and TM7 (the seventh transmembrane domain), as proven by direct Edman degradation sequencing. When this fragment was modified by the replacement of Val342 with Met to generate an additional site of cyanogen bromide cleavage, the labeled fragment was reduced in apparent size consistent with its representing the carboxyl-terminal portion of this fragment. Radiochemical sequencing of that fragment demonstrated covalent attachment of the probe to His347 and Leu348 in this domain. This represents the second experimentally demonstrated contact between a CCK analogue and this receptor, complementing the labeling of the domain just above TM1 (the first transmembrane domain) by a photolabile residue at the carboxyl terminus of CCK (Ji, Z. S., Hadac, E. M., Henne, R. M., Patel, S. A., Lybrand, T. P., and Miller, L. J. (1997) J. Biol. Chem. 272, 24393-24401). Both contacts are consistent with the conformational model of CCK binding proposed on the basis of the initial contact.

Original languageEnglish (US)
Pages (from-to)12988-12993
Number of pages6
JournalJournal of Biological Chemistry
Volume273
Issue number21
DOIs
StatePublished - May 22 1998

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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