A cysteine-linkable, short cleavable photoprobe with dual functionality to explore protein-protein interfaces

Area of Science:

• Chemical Biology
• Neuroscience
• Biochemistry

Background:

• Site-specific labeling is crucial for understanding protein function and interactions.
• Existing protein labeling techniques often lack precision or require complex synthesis.
• Developing novel photoprobes is essential for advancing molecular mapping studies.

Purpose of the Study:

• To develop a novel bifunctional photoprobe with dual photoactivatable species.
• To demonstrate site-specific labeling of a nicotinic acetylcholine receptor antagonist.
• To confirm the location of a snake alpha-neurotoxin analogue's functional site on the receptor.

Main Methods:

• Synthesis of a bifunctional photoprobe with an aryldiazonium group and a cleavable disulfide bond.
• Site-directed coupling of the photoprobe to a modified snake alpha-neurotoxin analogue.
• Photoactivation of the probe and subsequent labeling of the Torpedo acetylcholine receptor.
• Analysis of labeled receptor subunits and disulfide bond reduction for further characterization.

Main Results:

• The photoprobe successfully generated both arylcations and nitrenes upon irradiation.
• The modified neurotoxin acted as a reversible ligand and, upon 391 nm irradiation, labeled the alpha-subunit of the acetylcholine receptor.
• This confirmed the proximity of the toxin's second toxic loop to the receptor's alpha-subunit.
• Disulfide bond reduction allowed for subsequent radiolabeling of the target site.

Conclusions:

• The developed bifunctional photoprobe enables precise, site-directed labeling of proteins.
• This methodology accurately maps ligand-receptor interactions and protein binding sites.
• The approach facilitates further characterization of labeled biomolecules without requiring pre-synthesized radioactive probes.