Further evidence for a C-terminal structural motif in CCK
2
receptor active peptide hormones
Shane R. Stone
a
, Craig Giragossian
b
, Dale F. Mierke
b
, Graham E. Jackson
a,
*
a
Department of Chemistry, University of Cape Town, Private Bag, Rondebosch 7701, Cape Town, South Africa
b
Department of Molecular Pharmacology, Division of Biology and Medicine, Brown University, 171 Meeting Street, Providence, RI 02912, USA
1. Introduction
Gastrin and cholecystokinin are related peptide hormones
which share a common C-terminal pentapeptide sequence of
Gly-Trp-Met-Asp-Phe-NH
2
. Both hormones are able to activate
the CCK
2
receptor [49,51,68,69], whose principal pharmaco-
phore is the shared amidated C-terminal tetrapeptide
sequence [65].
Both gastrin and cholecystokinin are found in the gut
[43,68], where they play important roles in digestion and
gastric physiology. Gastrin is a central hormone in the
complex acid secretion pathway, initiating acid secretion by
peptides 28 (2007) 2211–2222
article info
Article history:
Received 21 May 2007
Received in revised form
7 September 2007
Accepted 10 September 2007
Published on line 22 September 2007
Keywords:
Gastrin
Cholecystokinin
CCK
2
Structural motif
Type I b-turn
NMR
Membrane-mimetic media
Micelles
Dodecylphosphocholine
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 dodecylphospho-
choline 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 a-helix spanning the Ala
11
-
Trp
14
sequence and an inverse g-turn centered on Nle
15
while that of [Tyr
9
-SO
3
] cholecys-
tokinin-15 contained a short 3
10
helix spanning its Met
10
to Met
13
sequence and an inverse
g-turn centered on Asp
14
. Significantly, both the C-terminal helices were found to terminate
in type I b-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.
# 2007 Elsevier Inc. All rights reserved.
* Corresponding author
. Tel.: +27 21 650 2531; fax: +27 21 689 7499.
E-mail address: Graham.Jackson@uct.ac.za (G.E. Jackson).
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/peptides
0196-9781/$ – see front matter # 2007 Elsevier Inc. All rights reserved.
doi:10.1016/j.peptides.2007.09.008