Determining Membrane Protein Topology Using Fluorescence Protease Protection (FPP)

Area of Science:

• Cell Biology
• Biochemistry
• Molecular Biology

Background:

• Integral membrane protein topology and orientation are critical for cellular function.
• Establishing this information for many membrane proteins remains challenging.
• Existing methods often require specific antibodies or large protein quantities.

Purpose of the Study:

• To present a simple and effective technique for determining membrane protein topology and orientation in living cells.
• To offer an alternative to existing methods that overcomes common limitations.

Main Methods:

• The fluorescence protease protection (FPP) assay utilizes green fluorescent protein (GFP) tagged membrane proteins.
• Selective cell permeabilization with digitonin allows differential protease access.
• Protease degrades exposed GFP, while organelle-protected GFP remains intact, revealing topology.

Main Results:

• The FPP method successfully determines membrane protein topology and orientation.
• It is applicable to various cell types and subcellular organelles (mitochondria, Golgi, ER, endosomes).
• The technique does not require multiple antibodies or large protein amounts and works in living cells.

Conclusions:

• Fluorescence protease protection (FPP) is a rapid, versatile, and accessible method for studying membrane protein topology.
• This technique simplifies the investigation of membrane protein structure-function relationships.
• FPP offers significant advantages for research in cell biology and biochemistry.