A processing enzyme cleaving avian progastrin at post-Phe bonds

Area of Science:

• Biochemistry
• Molecular Biology
• Endocrinology

Background:

• Neuroendocrine peptides undergo endoproteolytic processing from precursor forms.
• Cleavage typically occurs at mono- and dibasic residues, but other sites exist.
• Post-phenylalanine (post-Phe) cleavage was previously suggested for chicken progastrin processing.

Purpose of the Study:

• To characterize the post-Phe cleavage mechanism in chicken progastrin processing.
• To validate the existence and function of endoproteases cleaving at post-Phe sites in vertebrates.

Main Methods:

• Production of antibodies for radioimmunoassay and immunocytochemistry.
• Measurement of gastrin processing products in antral extracts.
• Immunohistochemical colocalization studies in antral G-cells.
• Identification of specific peptide fragments.

Main Results:

• High concentrations of gastrin-53 N-terminus and C-terminus were detected in antral extracts.
• Gastrin-30 N-terminus and a specific C-terminal fragment of gastrin-53 were also identified.
• Immunohistochemistry confirmed the colocalization of these fragments in G-cells.
• The intact N-terminal fragment complementary to gastrin-30 was identified, confirming Phe(23)-Ala(24) cleavage.

Conclusions:

• The study provides strong evidence for endoproteolytic cleavage at post-Phe sites in vertebrate hormone precursors.
• This research elucidates a novel mechanism in neuroendocrine peptide maturation.
• The findings expand our understanding of post-translational modifications in peptide hormone processing.