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제127회 대한화학회 학술발표회 및 총회 Unwinding Mechanism of Replicative Helicases: Lessons from Papillomavirus E1 Helicase

2021년 2월 18일 14시 56분 41초
PHYS1-3 이곳을 클릭하시면 발표코드에 대한 설명을 보실 수 있습니다.
목 11시 : 20분
Physical Chemistry - Recent Research Trends in Biophysical Chemistry
저자 및
Mina Lee
Safety Measurement Institute, Korea Research Institute of Standards and Science, Korea
Ring-shaped replicative helicases are hexameric helicases that play a key role in cellular DNA replication. The replicative helicases elaborately cooperate with a multi-enzyme complex synthesizing DNA at the replication fork. Despite intensive efforts to understand this fundamental biological process, the unwinding mechanism of replicative helicases still remains unclear. Bovine papillomavirus (BPV) E1 is one of the best-known model systems for complicated eukaryotic replicative helicases. E1 is a versatile stand-alone helicase that senses and melts the viral origin (ori) and unwinds DNA. Here, we present the unwinding mechanism of E1 studied using magnetic tweezers. The results obtained with forked DNA reveal that E1 as a single hexamer (SH) is a poor helicase with low processivity and unwinding rate. The negative effect of tension on unwinding indicates that there is a strong interaction between the helicase and the non-translocating DNA strand. From high force experiments, it was found that E1 unwinds DNA while encircling both DNA strands. Next, we investigated unwinding of dsDNA with ori, where E1 has been known to be assembled as a double hexamer. Unwinding activity for the dsDNA with ori was highly dependent on the applied force; while it hardly changed at high forces, the extension rapidly decreased at low forces. Strong activity at low forces suggests that the double hexamer does not separate into two SHs during unwinding. This is, surprisingly, the opposite of what has been generally believed about replicative helicases. Robust unwinding of double hexameric E1 suggests that dimerization of SHs greatly boosts unwinding activity of E1.