10 February 2016

The unwinding of the DNA helix was compared to oil production

Roman Fishman, N+1

Updated data on the structure of helicase, an enzyme that "unwinds" the DNA double helix, showed that this molecular machine can work in the manner of an oil rig, rocking the "rocker" back and forth. The results of the study are published by the journal Nature Structural & Molecular Biology (Yuan et al., Structure of the eukaryotic replicative CMG helicase suggests a pumpjack motion for translocation), they are also reported by the press release of the Brookhaven National Laboratory of the US Department of Energy (Scientists Propose "Pumpjack" Mechanism for Splitting and Copying DNA).

The double strand of DNA is a tense structure, and to work with it, the spiral needs to be "unraveled" by separating the chains connected by hydrogen bonds. This task is performed by helicase enzymes, which are involved in DNA replication (copying), and in its repair ("repair"), and in transcription (reading information for the synthesis of matrix RNA), and in many other vital processes. Scientists from the Brookhaven Laboratory, Rockefeller University and the State University of New York at Stony Brook established the spatial structure of CMG-helicase of yeast using cryo-electron microscopy.

Recently, this method has become increasingly popular, since it does not require a long, time-consuming and often intuitive process of obtaining protein crystals, and can consider molecules directly in solution. After a number of improvements made it possible to bring the resolution of cryo-electron microscopy to a level accessible to traditional X-ray diffraction analysis, such work is becoming more common. This time, the scientists managed to obtain structural data with an impressive resolution of up to 3.7 angstroms.

By itself, CMG helicase is a highly conserved and complex complex, including 11 separate protein domains, similar in archaea and eukaryotes. The name of the helicase is formed from the names of these domains, six of which (Mcm2-7) form two rings that span a single strand of DNA. They are flexibly linked to the Cdc45 domain and the GINS complex consisting of four domains, which are involved in binding other enzymes necessary, for example, for replication.

As scientists have found out, the enzyme can switch between two alternative conformations, so that one of the rings of the Mcm2-7 structure swings on a fixed base, like a rocker arm for oil production. Binding and hydrolysis of ATP gives this complex energy for the first movement: the ring of Mcm2-6-4 domains takes a "step forward" along the DNA helix, separating its strands. Then the hydrolyzed ADP is separated, and the helicase returns to its original conformation, in which the remaining domains catch up with the ones ahead.

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