Pre-steady-state kinetics shows differences in processing of various DNA lesions by Escherichia coli...

Area of Science:

• Biochemistry
• Molecular Biology
• DNA Repair Mechanisms

Background:

• Formamidopyrimidine-DNA-glycosylase (Fpg), also known as MutM, is essential for excising oxidatively damaged purines, such as 8-oxoguanine (8-oxoG), from DNA.
• Fpg functions as both a DNA glycosylase and an apurinic/apyrimidinic (AP) lyase, initiating DNA base excision repair pathways.

Purpose of the Study:

• To investigate the dynamic conformational changes of Fpg protein during its catalytic cycle using pre-steady-state kinetic analysis.
• To elucidate the temporal relationship between Fpg conformational transitions and its DNA binding and catalytic activities.

Main Methods:

• Pre-steady-state kinetic analysis of Fpg on oligonucleotide duplexes containing 8-oxo-2'-deoxyguanosine, abasic sites, or tetrahydrofuran analogues.
• Monitoring Fpg's intrinsic tryptophan fluorescence using stopped-flow experiments to detect protein conformational changes.

Main Results:

• Multiple (4-5) rapid conformational transitions (2 ms to 10 s) were observed in Fpg upon interaction with 8-oxoG and abasic site-containing DNA substrates.
• These fast transitions are associated with DNA binding and lesion recognition, leading to a catalytically competent enzyme conformation.
• Catalytic steps did not show discernible fluorescence changes, with only a single slow conformational change detected for cleavable substrates after 10 s.

Conclusions:

• Fpg protein undergoes several rapid, sequential conformational changes after substrate binding, which are critical for activating its catalytic function.
• The dynamic structural rearrangements highlight the intricate interplay between enzyme and DNA during the DNA repair process.