Structural requirements of pancreatic polypeptide receptor binding.

Area of Science:

• Biochemistry
• Molecular Biology
• Gastroenterology

Background:

• Pancreatic polypeptide (PP) receptors are present on the basolateral membranes (BLM) of canine intestinal mucosa.
• Understanding the structural basis of PP-receptor interaction is crucial for elucidating its physiological roles.

Purpose of the Study:

• To determine the specific structural requirements of the pancreatic polypeptide (PP) molecule for binding to its receptor.
• To investigate the role of different regions and modifications of PP in receptor recognition.

Main Methods:

• Utilized a radioreceptor assay with purified canine intestinal basolateral membranes (BLM).
• Tested binding affinities of various mammalian PP analogs and modified bovine PP (bPP) fragments.
• Assessed receptor cross-reactivities (CR) to different PP species and bPP fragments.

Main Results:

• Receptor binding affinity varied significantly across mammalian species, with bovine PP showing the highest CR (100%) and rat PP the lowest (3%).
• Specific fragments and N-terminal deletions of bPP showed minimal to no receptor binding (<0.1% CR).
• Modification of the COOH-terminal tyrosinamide (e.g., to free acid) abolished binding, while esterification partially restored it (60% CR). Oxidation of methionine-30 also reduced binding (67% CR).

Conclusions:

• The primary structure of pancreatic polypeptide (PP) is essential for full receptor binding.
• Both the NH2- and COOH-terminal regions of PP are critical for receptor recognition.
• The integrity of the COOH-terminal tyrosinamide is indispensable for PP binding to its receptor.