Single-molecule analysis of restriction DNA fragments using fluorescence correlation spectroscopy

Area of Science:

• Biochemistry
• Molecular Biology
• Analytical Chemistry

Background:

• Restriction enzymes are crucial tools for DNA manipulation.
• Monitoring enzymatic DNA cleavage in real-time is essential for understanding enzyme kinetics and optimizing molecular biology protocols.
• Fluorescence correlation spectroscopy (FCS) offers high sensitivity for analyzing molecular dynamics in small volumes.

Purpose of the Study:

• To apply fluorescence correlation spectroscopy (FCS) for real-time monitoring of DNA cleavage by four different restriction enzymes.
• To develop a practical method for quantifying the number of molecules during FCS measurements of enzymatic reactions.
• To compare the digestion kinetics of HaeIII, HgaI, BsmAI, and BspMI on M13 DNA.

Main Methods:

• Utilizing fluorescence-labeled M13 DNA (7250 bp) as the substrate.
• Employing fluorescence correlation spectroscopy (FCS) in a microvolume (1.5 x 10(-15) L).
• Analyzing the decrease in fluorescence correlation function amplitude to monitor DNA hydrolysis.
• Deriving a practical equation for estimating molecule numbers in FCS experiments.

Main Results:

• HaeIII and BsmAI completely digested the DNA within 8 hours under standard conditions.
• HgaI and BspMI exhibited slower digestion kinetics, requiring over 40 hours for completion.
• The decrease in FCS amplitude directly correlated with the extent of DNA hydrolysis.
• Differences in enzyme kinetics may be attributed to nucleotide insertions between recognition and cleavage sites.

Conclusions:

• FCS is a powerful technique for real-time monitoring of DNA restriction enzyme activity.
• Enzyme digestion rates vary significantly, with some enzymes showing considerably slower kinetics.
• The developed FCS method provides quantitative insights into DNA hydrolysis processes.
• Understanding enzyme kinetics aids in selecting appropriate enzymes for molecular biology applications.