Enhanced Site-Specific Fluorescent Labeling of Membrane Proteins Using Native Nanodiscs.

Area of Science:

• Biophysics
• Structural Biology
• Biochemistry

Background:

• Fluorescent labeling is crucial for studying membrane protein functions, signaling, interactions, and dynamics.
• Organic fluorophores offer good photophysical properties and photostability for labeling.
• Site-specific labeling is hindered by the inaccessibility of surface-exposed cysteine residues within detergent micelles.

Purpose of the Study:

• To develop a novel method for overcoming the challenge of inaccessible cysteine residues in membrane proteins for fluorescent labeling.
• To enable fluorescent labeling of membrane proteins in a native-like lipid-bilayer environment.
• To demonstrate the versatility of the technique with difficult-to-label membrane proteins.

Main Methods:

• Developed polymer-encapsulated nanodiscs to maintain a native-like membrane environment for proteins.
• Utilized His-tagged proteins within nanodiscs, retained on a nickel affinity column.
• Performed simultaneous purification and fluorescent labeling by adding organic dyes.

Main Results:

• Successfully achieved fluorescent labeling of membrane proteins, including the potassium channel KvAP and urea channel HpUreI.
• Demonstrated that the developed method overcomes limitations of previous detergent-based labeling approaches.
• Ensured accessibility of surface-exposed cysteine residues for site-specific labeling.

Conclusions:

• The polymer-encapsulated nanodisc method provides a versatile approach for fluorescently labeling challenging membrane proteins.
• This technique allows for studying membrane proteins in near-native states, advancing biophysical and structural studies.
• Opens new avenues for drug discovery and understanding membrane protein mechanisms.