A "Smart" ¹²⁸Xe NMR Biosensor for pH-Dependent Cell Labeling.

Area of Science:

• Biophysical Chemistry
• Chemical Biology
• Nuclear Magnetic Resonance (NMR) Spectroscopy

Background:

• Peptide conformational changes are crucial for biological function.
• Developing sensitive probes for acidic environments is important for biological and medical applications.
• Xenon-129 NMR offers unique properties for molecular imaging and sensing.

Purpose of the Study:

• To create a "smart" xenon-129 NMR biosensor.
• To utilize peptide conformational changes for pH-dependent cell labeling.
• To explore the application of this biosensor in acidic environments and for cancer diagnosis.

Main Methods:

• Conjugation of a 30mer EALA-repeat peptide to a cryptophane host molecule.
• Characterization of pH-dependent peptide conformation (α-helical at pH 5.5, disordered at pH 7.5).
• Measurement of xenon-129 NMR chemical shifts and hyper-polarized chemical exchange saturation transfer (hyper-CEST) NMR.

Main Results:

• The xenon-129 NMR chemical shift showed a strong pH dependence (Δδ = 3.4 ppm).
• Peptidocryptophane detection limits were as low as 10(-11) M, significantly lower than other NMR pH reporters.
• Peptide-cell membrane insertion at pH 5.5 induced a substantial 13.4 ppm downfield shift in the cryptophane-(129)Xe NMR signal.

Conclusions:

• The developed xenon-129 NMR biosensor effectively detects pH changes through peptide conformational transitions.
• This technology enables ultrasensitive probing of peptide structure and function.
• Potential applications include pH-dependent cell labeling for cancer diagnosis and treatment monitoring.