Deciphering the subunit composition of multimeric proteins by counting photobleaching steps.

Area of Science:

• Biophysics
• Molecular Biology
• Optical Microscopy

Background:

• Subdiffraction imaging resolution is limited to 20 nm, hindering the study of small protein complexes (2-5 nm).
• Directly resolving individual subunits within these small complexes using conventional optical methods is challenging.

Purpose of the Study:

• To provide an overview of single-molecule subunit counting techniques for protein complexes.
• To guide researchers in applying single-molecule subunit counting to their studies.
• To detail methods for immobilizing and labeling proteins for subunit analysis.

Main Methods:

• Observation of photobleaching steps of individual fluorophores.
• Co-localization of single-molecule fluorescence emission in multiple colors.
• Immobilization and labeling of protein complexes.

Main Results:

• Demonstration of resolving the number and stoichiometry of subunits in immobilized protein complexes.
• Overview of various proteins successfully investigated using this approach.
• Compilation of different immobilization and labeling techniques.

Conclusions:

• Single-molecule subunit counting is a viable method to determine protein complex composition.
• This technique overcomes the spatial resolution limitations of traditional optical imaging.
• The review serves as a practical guide for implementing subunit counting in research.