Nucleic acid unwinding by hepatitis C virus and bacteriophage t7 helicases is sensitive to base pair stability.
Helicases are motor enzymes that convert the chemical energy of NTP hydrolysis into mechanical force for motion and nucleic acid strand separation. Within the cell, helicases process a range of nucleic acid sequences. It is not known whether this composite rate of moving and opening the strands of nucleic acids depends on the base sequence. Our presteady state kinetic studies of helicases from two classes, the ring-shaped T7 helicase and two forms of non-ring-shaped hepatitis C virus (HCV) helicase, show that both the unwinding rate and processivity depend on the sequence and decrease as the nucleic acid stability increases. The DNA unwinding activity of T7 helicase and the RNA unwinding activity of HCV helicases decrease steeply with increasing base pair stability. On the other hand, the DNA unwinding activity of HCV helicases is less sensitive to base pair stability. These results predict that helicases will fall into a spectrum of modest to high sensitivity to base pair stability depending on their biological role in the cell. Modeling of the dependence provided the degree of the active involvement of helicase in base pair destabilization during the unwinding process and distinguished between passive and active mechanisms of unwinding.
Donmez
Ilker
I
Department of Biochemistry, University of Medicine and Dentistry, New Jersey, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA.
Rajagopal
Vaishnavi
V
Jeong
Yong-Joo
YJ
Patel
Smita S
SS
D017123:Bacteriophage T7 / Q000201:enzymology*; D002384:Catalysis; D003001:Cloning, Molecular; D004247:DNA / Q000737:chemistry; D019915:DNA Primase / Q000737:chemistry*; D004279:DNA, Viral / Q000737:chemistry; D016174:Hepacivirus / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D015233:Models, Statistical; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D009696:Nucleic Acids / Q000737:chemistry*; D013816:Thermodynamics; D013997:Time Factors
D004279:DNA, Viral; D009696:Nucleic Acids; D004247:DNA; D019915:DNA Primase