Protein folding is a quantum transition

In 1981, in the first technical paper on molecular engineering as a route toward general systems for manufacturing with atomic precision, Eric Drexler proposed that the engineering problem of designing proteins to fold in a predetermined way is much easier than the scientific problem of predicting how natural proteins fold. Progress two years ago in designing a completely new protein from scratch (see this Nanodot post and this Metamodern post by Dr.Drexler) vindicated the original proposal and confirmed the viability of the protein engineering path toward advance nanotechnology. Now a paradigm shift in understanding the scientific problem of protein folding, in particular the temperature dependence of protein folding, amounts to, in the words of one knowledgeable commenator, “the first universal laws of protein folding”. With thanks to KurzweilAI, from The Physics arXiv Blog “Physicists Discover Quantum Law of Protein Folding“:

Quantum mechanics finally explains why protein folding depends on temperature in such a strange way.

The famous Arrhenius relationship states that things happen faster as they got hotter. In chemistry, that’s generally true but there’s an important exception: the speed at which proteins fold into their functional shape.

It’s easy to think that proteins ought to fold more quickly as they cool down and then unfold more quickly as they heat up. But the actual relationship is both nonlinear and asymmetric, meaning that unfolding is not the reverse of folding.

Molecular biologists have put forward various mechanisms to explain this, such as the nonlinear interaction between water and hydrophobic parts of proteins. But none of these are very convincing.

That looks set to change with the work of Liaofu Luo at the Inner Mongolia University and Jun Lu at the Inner Mongolia University of Technology, both in China. They say that the way folding depends on temperature all becomes clear as soon as you take quantum mechanics into account. …

Today, Luo and Lo say these curves can be easily explained if the process of folding is a quantum affair. By conventional thinking, a chain of amino acids can only change from one shape to another by mechanically passing though various shapes in between.

But Luo and Lo say that if this process were a quantum one, the shape could change by quantum transition, meaning that the protein could ‘jump’ from one shape to another without necessarily forming the shapes in between.

Luo and Lo explore this idea using a mathematical model of how this would work and then derive equations that describe how the rate of “quantum folding” would change with temperature. Finally they fit the predictions of their model to some real world experiments.

Their astonishing result is that this quantum transition model fits the folding curves of 15 different proteins and even explains the difference in folding and unfolding rates of the same proteins.

That’s a significant breakthrough. Luo and Lo’s equations amount to the first universal laws of protein folding. That’s the equivalent in biology to something like the thermodynamic laws in physics.

The research paper can be downloaded from arXiv: arXiv:1102.3748v1. The question for the protein engineering path to advanced nanotechnology is, will this “move outside the realm of classical physics”, in the words of the paper’s abstract, help or hinder efforts to design proteins from scratch to fold in a predetermined way?

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