Structure of a precursor to human pancreatic polypeptide

Area of Science:

• Endocrinology
• Molecular Biology
• Biochemistry

Background:

• Pancreatic polypeptide is a key hormone involved in gastrointestinal regulation.
• Understanding the synthesis and processing of pancreatic polypeptide is crucial for comprehending islet cell function and related disorders.

Purpose of the Study:

• To isolate and characterize the precursor of human pancreatic polypeptide.
• To determine the complete amino acid sequence of the pancreatic polypeptide precursor.
• To elucidate the structural organization and potential processing sites of the precursor.

Main Methods:

• Isolation of messenger RNA (mRNA) from human pancreatic islet cell tumors.
• Cell-free translation of mRNA to identify precursor proteins.
• Construction and screening of a complementary DNA (cDNA) library.
• Nucleotide sequencing of cDNA to deduce amino acid sequences.
• Analysis of protein sequences and Edman degradation for structural confirmation.

Main Results:

• Identified a precursor of pancreatic polypeptide (pre-pro-pancreatic polypeptide) with an approximate Mr of 11,000.
• Deduced the complete amino acid sequence of pre-pro-pancreatic polypeptide, comprising 95 residues (Mr = 10,432).
• The mature pancreatic polypeptide sequence is centrally located, preceded by a hydrophobic leader sequence and followed by a carboxyl-terminal extension similar to canine islet peptides.
• A smaller, processed form of the polypeptide was generated, with pancreatic polypeptide sequence at its amino terminus.

Conclusions:

• Human pancreatic polypeptide is synthesized as a larger precursor, pre-pro-pancreatic polypeptide.
• The precursor contains a signal peptide and a carboxyl-terminal flanking peptide, suggesting a specific processing pathway.
• These findings provide critical insights into the molecular basis of pancreatic polypeptide synthesis and regulation.