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Differences in receptor binding and stability to enzymatic digestion between CCK-8 and CCK-58
Joseph R Reeve1, Douglas C McVey, Nigel W Bunnett
1CURE Digestive Diseases Research Center, VAGLAHS, Los Angeles, CA 90073, USA. jreeve@ucla.edu
Pancreas
|October 9, 2002
Summary
The carboxyl-terminal tertiary structure of cholecystokinin-58 (CCK-58) enhances binding to CCK-A receptors and increases stability against enzymatic digestion compared to cholecystokinin-8 (CCK-8). These structural differences influence receptor interactions and peptide degradation.
Area of Science:
- Endocrinology
- Neuroscience
- Biochemistry
Background:
- Cholecystokinin (CCK) is a peptide hormone with various physiological roles, including regulation of pancreatic secretion and satiety.
- CCK exists in multiple forms, with CCK-8 and CCK-58 being significant variants differing in length and potentially structure.
- The tertiary structure of the C-terminus is hypothesized to influence CCK's biological activity and receptor interactions.
Purpose of the Study:
- To investigate whether distinct tertiary structures of the C-terminus of CCK-8 and CCK-58 lead to differences in pancreatic amylase secretion stimulation.
- To evaluate the binding affinities of CCK-8 and CCK-58 to CCK-A and CCK-B receptors.
- To assess the stability of CCK-8 and CCK-58 to enzymatic digestion as an indicator of structural differences.
Main Methods:
- Purification of canine CCK-58 from intestinal extracts and acquisition of CCK-8.
- Quantification of peptide amounts using amino acid analysis.
- Assessment of receptor binding using membrane preparations from mouse pancreas (CCK-A receptors) and brain (CCK-B receptors).
- Evaluation of enzymatic stability by exposing CCK-8 and CCK-58 to endopeptidase 24:11.
Main Results:
- CCK-58 demonstrated three times greater potency than CCK-8 in binding to mouse pancreatic CCK-A receptors.
- CCK-58 and CCK-8 exhibited equipotency in binding to mouse brain CCK-B receptors.
- CCK-8 was rapidly digested by endopeptidase 24:11, while CCK-58 remained largely undigested.
Conclusions:
- The findings strongly support the hypothesis that differences in the C-terminal tertiary structure of CCK-8 and CCK-58 significantly impact their interaction with CCK receptors.
- The distinct tertiary structures also confer differential stability against enzymatic degradation, with CCK-58 being more resistant.
- These structural variations likely contribute to the differential physiological effects observed for various CCK peptide forms.