TY - JOUR
T1 - The role of segment 32-47 of cholecystokinin receptor type A in CCK8 binding
T2 - Synthesis, nuclear magnetic resonance, circular dichroism and fluorescence studies
AU - De Luca, Stefani
AU - Ragone, Raffaele
AU - Bracco, Chiara
AU - Digilio, Giuseppe
AU - Tesauro, Diego
AU - Saviano, Michele
AU - Pedone, Carlo
AU - Morelli, Giancarlo
PY - 2003/3/1
Y1 - 2003/3/1
N2 - The segment 32-47 of the N-terminal extracellular domain of the type A cholecystokinin receptor, CCKA-R(32-47), was synthesized and structurally characterized in a membrane mimicking environment by CD, NMR and molecular dynamics calculations. The region of CCKA-R(32-47) encompassing residues 39-46 adopted a well-defined secondary structure in the presence of DPC micelles, whereas the conformation of the N-terminal region (segment 32-37) could not be uniquely defined by the NOE derived distance constraints because of local flexibility. The conformation of the binding domain of CCKA-R(32-47) was different from that found for the intact N-terminal receptor tail, CCKA -R(1-47). To assess whether CCKA-R(32-47) was still able to bind the nonsulfated cholecystokinin C-terminal octapeptide, CCK8, a series of titrations was carried out in SDS and DPC micelles, and the binding interaction was followed by fluorescence spectroscopy. These titrations gave no evidence for complex formation, whereas a high binding affinity was found between CCKA-R(1-47) and CCK8. The different affinities for the ligand shown by CCKA-R(32-47) and CCKA-R(1-47) were paralleled by different interaction modes between the receptor segments and the micelles. The interaction 6of CCKA-R(32-47) with DPC micelles was much weaker than that of CCKA-R(1-47), because the former receptor segment lacks proper stabilizing contacts with the micelle surface. In the case of SDS micelles CCKA-R(32-47) was found to form non-micellar adducts with the detergent that prevented the onset of a functionally significant interaction between the receptor segment and the micelle. It is concluded that tertiary structure interactions brought about by the 1-31 segment play a key role in the stabilization of the membrane bound, biologically active conformation of the N-terminal extracellular tail of the CCKA receptor.
AB - The segment 32-47 of the N-terminal extracellular domain of the type A cholecystokinin receptor, CCKA-R(32-47), was synthesized and structurally characterized in a membrane mimicking environment by CD, NMR and molecular dynamics calculations. The region of CCKA-R(32-47) encompassing residues 39-46 adopted a well-defined secondary structure in the presence of DPC micelles, whereas the conformation of the N-terminal region (segment 32-37) could not be uniquely defined by the NOE derived distance constraints because of local flexibility. The conformation of the binding domain of CCKA-R(32-47) was different from that found for the intact N-terminal receptor tail, CCKA -R(1-47). To assess whether CCKA-R(32-47) was still able to bind the nonsulfated cholecystokinin C-terminal octapeptide, CCK8, a series of titrations was carried out in SDS and DPC micelles, and the binding interaction was followed by fluorescence spectroscopy. These titrations gave no evidence for complex formation, whereas a high binding affinity was found between CCKA-R(1-47) and CCK8. The different affinities for the ligand shown by CCKA-R(32-47) and CCKA-R(1-47) were paralleled by different interaction modes between the receptor segments and the micelles. The interaction 6of CCKA-R(32-47) with DPC micelles was much weaker than that of CCKA-R(1-47), because the former receptor segment lacks proper stabilizing contacts with the micelle surface. In the case of SDS micelles CCKA-R(32-47) was found to form non-micellar adducts with the detergent that prevented the onset of a functionally significant interaction between the receptor segment and the micelle. It is concluded that tertiary structure interactions brought about by the 1-31 segment play a key role in the stabilization of the membrane bound, biologically active conformation of the N-terminal extracellular tail of the CCKA receptor.
KW - CCK receptor
KW - CCK8 binding
KW - Fluorescence
KW - NMR
UR - http://www.scopus.com/inward/record.url?scp=0037348685&partnerID=8YFLogxK
U2 - 10.1002/psc.442
DO - 10.1002/psc.442
M3 - Article
SN - 1075-2617
VL - 9
SP - 156
EP - 169
JO - Journal of Peptide Science
JF - Journal of Peptide Science
IS - 3
ER -