Quantifying Lysosomal Degradation of Extracellular Proteins With a Fluorescent Protein-Based Internalization Assay

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Endocytosis is a vital cellular process for nutrient uptake, signaling, and waste removal.
• Quantitative methods for analyzing lysosomal degradation of extracellular proteins via endocytosis are limited.
• Existing methods lack the precision needed for detailed analysis of protein internalization and degradation pathways.

Purpose of the Study:

• To develop and validate a novel protocol for the quantitative analysis of extracellular protein internalization and lysosomal degradation.
• To establish a robust method for tracking protein trafficking within cells using a tandem fluorescent reporter system.
• To provide a broadly applicable tool for studying endocytosis and its role in cellular processes.

Main Methods:

• Purification of a protein-of-interest (POI)-red fluorescent protein (RFP)-green fluorescent protein (GFP) fusion protein from mammalian cell culture supernatant.
• Quantitative assessment of POI-RFP-GFP internalization using flow cytometry to measure GFP and RFP fluorescence signals.
• Confirmation of lysosomal degradation of the POI-RFP-GFP construct via immunoblotting techniques.

Main Results:

• Successful purification of the modified POI-RFP-GFP fusion protein.
• Demonstrated quantification of protein internalization based on distinct RFP and GFP signal intensities.
• Validated lysosomal degradation of the internalized protein through biochemical assays.

Conclusions:

• The developed protocol offers a reliable method for quantifying extracellular protein internalization and lysosomal degradation.
• This technique enhances the study of endocytosis and protein trafficking in mammalian cells.
• The method is versatile and applicable to various extracellular proteins and cellular modifications.