A new paper just published in the journal Science reveals how an SMC (structural maintenance of chromosome) complex called MukBEF “climbs” DNA in a manner similar to a rock-climber grabbing onto a handhold.
The paper reports,
Although ATP hydrolysis is essential for the activity of SMC complexes, its mechanistic importance has been unclear. Our data indicate that the minimal functional MukBEF complex acting at discrete chromosome positions is an ATP-bound dimer of MukB dimers, with ATP binding and head engagement being necessary for stable chromosome association and ATP hydrolysis required to release complexes from chromosomes. The observation that turnover of MukBEF complexes from chromosomes is slower than predicted from in vitro adenosine triphosphatase (ATPase) levels supports a model where ATP hydrolysis within each ATPase head pair is independent, with all four ATP molecules in the two closed dimer heads needing to be hydrolyzed almost simultaneously to completely release a single DNA-bound complex. A multimeric form of MukBEF would therefore allow release of one DNA segment and capture of a new segment without releasing the complex from the chromosome, a process akin to a rock climber making trial grabs to reach a hand hold, and one which could lead to ordered MukBEF movement within a chromosome, perhaps leading to DNA remodelling. This is analogous to the processive “walking” of the molecular motors kinesin and dynein along microtubules.
Science Daily also reported on the research, noting that “This opening and closing action of the machine is essentially a process of mechanical ‘grabbing’, in which it attempts to seize more free DNA, like the rock-climber searching for a new handhold.”
Molecular motors such as this represent biology at its finest and exhibit clear evidence of design.