A fluorescence assay for geranylgeranyl transferase type I

Area of Science:

• Biochemistry
• Enzymology
• Fluorescence Assays

Background:

• Geranylgeranyl transferase (GGTase) is a key enzyme in protein prenylation.
• Accurate measurement of GGTase activity is crucial for understanding its biological roles and developing inhibitors.
• Existing assays often rely on radiolabeled substrates or purified recombinant proteins, which can be cumbersome and expensive.

Purpose of the Study:

• To develop and characterize a new, non-radioactive fluorescence assay for quantifying geranylgeranyl transferase (type I) activity.
• To evaluate the utility of novel fluorescent substrates in GGTase activity assays.
• To determine kinetic parameters and inhibitory effects using the developed assay.

Main Methods:

• A fluorescence assay was developed using Dansyl GCVLL as a fluorescent substrate and unlabeled geranylgeranyl diphosphate.
• Enzyme kinetics were determined by varying substrate concentrations.
• The inhibitory effect of CVFL on GGTase activity was assessed.

Main Results:

• The assay successfully measured geranylgeranyl transferase (type I) activity without requiring radiolabeled substrates or purified Ras protein.
• The Michaelis constants (Km) for Dansyl GCVLL and geranylgeranyl diphosphate were determined to be 5 µM and 800 nM, respectively.
• Dansyl GCVLL demonstrated higher enzymatic activity compared to Dansyl GCVII at equimolar concentrations, while Dansyl GCVLS (a farnesyl transferase substrate) was inactive.
• CVFL acted as a competitive inhibitor with a Ki of 200 nM.

Conclusions:

• A novel, sensitive, and efficient fluorescence assay for geranylgeranyl transferase (type I) activity has been established.
• This assay provides a valuable tool for biochemical studies of GGTase and for screening potential inhibitors.
• The findings highlight the potential of fluorescently labeled peptides as substrates for enzyme activity assays.