title: Further evidence for a C-terminal structural motif in CCK2 receptor active peptide hormones.
abstract: A comparison of the conformational characteristics of the related hormones [Nle(15)] gastrin-17 and [Tyr(9)-SO(3)] cholecystokinin-15, in membrane-mimetic solutions of dodecylphosphocholine micelles and water, was undertaken using NMR spectroscopy to investigate the possibility of a structural motif responsible for the two hormones common ability to stimulate the CCK(2) receptor. Distance geometry calculations and NOE-restrained molecular dynamics simulations in biphasic solvent boxes of decane and water pointed to the two peptides adopting near identical helical C-terminal configurations, which extended one residue further than their shared pentapeptide sequence of Gly-Trp-Met-Asp-Phe-NH(2). The C-terminal conformation of [Nle(15)] gastrin-17 contained a short alpha-helix spanning the Ala(11)-Trp(14) sequence and an inverse gamma-turn centered on Nle(15) while that of [Tyr(9)-SO(3)] cholecystokinin-15 contained a short 3(10) helix spanning its Met(10) to Met(13) sequence and an inverse gamma-turn centered on Asp(14). Significantly, both the C-terminal helices were found to terminate in type I beta-turns spanning the homologous Gly-Trp-Met-Asp sequences. This finding supports the hypothesis that this structural motif is a necessary condition for CCK(2) receptor activation given that both gastrin and cholecystokinin have been established to follow a membrane-associated pathway to receptor recognition and activation. Comparison of the conformations for the non-homologous C-terminal tyrosyl residues of [Nle(15)] gastrin-17 and [Tyr(9)-SO(3)] cholecystokinin-15 found that they lie on opposite faces of the conserved C-terminal helices. The positioning of this tyrosyl residue is known to be essential for CCK(1) activity and non-essential for CCK(2) activity, pointing to it as a possible differentiator in CCK(1)/CCK(2) receptor selection. The different tyrosyl orientations were retained in molecular models for the [Nle(15)] gastrin-17/CCK(2) receptor and [Tyr(9)-SO(3)] cholecystokinin-15/CCK(1) receptor complexes, highlighting the role of this residue as a likely CCK(1)/CCK(2) receptor differentiator.
authors.affiliation: Department of Chemistry, University of Cape Town, Rondebosch 7701, Cape Town, South Africa.
authors.forename: Shane R
authors.initials: SR
authors.lastname: Stone
authors.forename: Craig
authors.initials: C
authors.lastname: Giragossian
authors.forename: Dale F
authors.initials: DF
authors.lastname: Mierke
authors.forename: Graham E
authors.initials: GE
authors.lastname: Jackson
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D002766:Cholecystokinin / Q000737:chemistry / Q000378:metabolism; D005755:Gastrins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010767:Phosphorylcholine / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D043887:Receptor, Cholecystokinin B / Q000737:chemistry* / Q000378:metabolism
chemical_list: D005755:Gastrins; D043887:Receptor, Cholecystokinin B; D010767:Phosphorylcholine; C028810:dodecylphosphocholine; C013550:gastrin 17; D002766:Cholecystokinin