Protonation-Driven Membrane Insertion of a pH-Low Insertion Peptide

Area of Science:

• Biophysics
• Membrane Protein Chemistry

Background:

• The pH-low insertion peptide (pHLIP) exhibits pH-dependent membrane insertion, showing promise for cancer therapy.
• Understanding the precise mechanism of pHLIP's pH-sensing and insertion is crucial for its optimization.

Purpose of the Study:

• To elucidate the pH-dependent membrane insertion mechanism of pHLIP.
• To identify the specific roles of aspartate/glutamate residues in protonation-driven insertion.
• To determine the location of the transmembrane helix within the pHLIP sequence.

Main Methods:

• Solid-state NMR spectroscopy to trace backbone conformations and determine residue-specific pKa values.
• Tryptophan fluorescence quenching to investigate intermediate states.

Main Results:

• The transmembrane helix spans residues A10 to D33, with a break between T19 and P20.
• Residue-specific pKa values (D31: 6.5, D33: 6.3, D25: 6.1, D14: 5.8) define the protonation sequence.
• Evidence for intermediate states disrupting membranes at pH 6.4 was observed.

Conclusions:

• Solid-state NMR successfully mapped the pHLIP transmembrane helix and identified key acidic residues governing its pH-triggered insertion.
• The determined pKa values provide a detailed molecular basis for pHLIP's function.
• The findings offer insights into pHLIP's potential applications in targeted therapies.