A pH-Induced Switch in Human Glucagon-like Peptide-1 Aggregation Kinetics

Area of Science:

• Biochemistry
• Biophysics
• Pharmaceutical Science

Background:

• Protein and peptide aggregation, including amyloid fibril formation, has significant implications in biotechnology, pharmaceuticals, and diseases.
• Human glucagon-like peptide-1 (GLP-1) is a crucial hormone for glucose regulation, with analogues widely used in type 2 diabetes treatment.

Purpose of the Study:

• To elucidate the aggregation and amyloid fibrillation mechanism of human glucagon-like peptide-1 (GLP-1).
• To investigate the pH-induced switch in GLP-1 aggregation kinetics and identify the underlying molecular determinants.

Main Methods:

• Monitoring amyloid fibril formation of GLP-1 using thioflavin T fluorescence across varying peptide concentrations and pH (7.5-8.2).
• Utilizing biophysical techniques to characterize aggregation initiation, fibril structure, and stability.
• Estimating pK_a values of ionizable groups to pinpoint pH-sensitive residues.

Main Results:

• A distinct pH-induced switch in GLP-1 aggregation kinetics was observed.
• At pH 8.2, kinetics align with a nucleation-polymerization model.
• At pH 7.5, unusual kinetics showed increased lag time with peptide concentration, attributed to off-pathway species and a slow monomer conversion step.

Conclusions:

• The N-terminus protonation/deprotonation is identified as the cause of the pH-induced switch in GLP-1 aggregation.
• Off-pathway species formation is favored under conditions promoting GLP-1 oligomerization.
• Understanding these aggregation mechanisms is vital for the safe and effective pharmaceutical use of GLP-1 analogues.