MRC National Institute for Medical Research, London
Science for Health
How a helicase works to unwind DNA
03 August 2009
Helicases are proteins that are responsible for separating the helical, double-stranded DNA into component single strands, ready for processes such as replication. PcrA is a helicase that plays this role in the replication of some promiscuous plasmids of certain bacteria, that contain antibiotic resistance genes. PcrA uses the energy of ATP hydrolysis to separate one base pair of DNA for each ATP used.
Martin Webb (pictured) and his laboratory in NIMR's Division of Physical Biochemistry has analysed how the biochemical processes that are required for ATP hydrolysis catalysed by a helicase are related to movement along the DNA. Using rapid-reaction and fluorescence techniques, they followed the individual process in real time. The chemical step of ATP cleavage is greatly accelerated when DNA is bound to the helicase, producing the high activation of this protein, although the cleavage remains slower than substrate binding and product release steps. The major transition in structure, leading to unidirectional movement along DNA, is very likely to occur during this cleavage step. The results help us to understand in general how this large family of helicases work, but also, in particular, how PcrA interacts with its partner protein, RepD, during plasmid replication.
This laboratory is measuring how PcrA operates as an ATP-coupled helicase in several ways by following its action in real time. The coupling of ATP hydrolysis to movement is an essential part of many motor proteins within the cell, including helicases, myosins and kinesins. Although many parts of PcrA function and structure are well understood, this work extends our understanding to how the chemistry of ATP hydrolysis relates to the mechanical process of translocation.
Martin Webb
Original Article
The research findings are published in full in:
Christopher P. Toseland, Maria M. Martinez-Senac, Andrew F. Slatter and Martin R. Webb (2009). The ATPase cycle of PcrA helicase and its coupling to translocation on DNA Journal of Molecular Biology , epub ahead of print. Publisher abstract
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