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The Information Physics of Life

Yasushi Okada, Team Leader, RIKEN (BDR), Professor, Graduate School of Medicine / Adjunct Professor, Department of Physics

I want to understand living organisms and life phenomena in the language of physics. This is the goal of the field of biophysics, which lies at the interface between biology and physics.

We have been studying a protein molecular motor called kinesin as a dynamical life phenomenon. Kinesin hydrolyzes adenosine triphosphate (ATP) and converts its chemical energy into mechanical work of intracellular mass transport. To investigate the mechanism of its operation, we have developed a microscope to directly observe and measure the movement of a single kinesin molecule.

Just as we are concerned about the fuel efficiency of a car, we are tempted to investigate the fuel efficiency of kinesin, i.e., the conversion efficiency from input energy to output work. However, thermodynamics and statistical mechanics cannot be simply applied to the discussion of efficiency at the level of a single molecule. Thermodynamics discusses the free energy change associated with hydrolysis based on the concentration of ATP. At the level of a single kinesin molecule, the concentration of ATP should be discussed as the probability of ATP binding to kinesin per unit time, and energies and so on are also subject to discussion based on probability.

The problem of simply applying thermodynamics to a system such as a single molecule has long been pointed out in thought experiments such as Maxwell's demon, but it has emerged as a realistic subject due to the development of biophysical experiments such as those described above. Against this background, research on statistical mechanics and thermodynamics for stochastic and nonequilibrium systems has progressed, resulting in "information thermodynamics.

In information thermodynamics, it is possible to discuss not only the single molecule level but also changing systems. The intuitive property that "more energy is needed to change the state quickly" can be formulated as a thermodynamic uncertainty relation. The framework is developing into one that allows quantitative discussion of the trade-off relationship between various functions and the energy (heat cost) required to realize them, such as "more energy is required to reduce errors.

Microscope developed for high-speed, high-resolution measurement of a single protein molecular motor

In this light, organisms may not have evolved with a focus on fuel efficiency alone. In fact, measurements using single molecule measurement techniques have reported that the energy conversion efficiency of kinesin is unexpectedly low. Kinesin may be consuming extra energy to realize some other function. What function is it?

As a result of the development of information thermodynamics in the form of explicitly incorporating information through Maxwell's demon argument, etc., it is expected to be possible to study life phenomena such as intracellular information processing using information thermodynamics as a starting point.

The problem of single molecule measurement of protein molecular motors has provided theorists with a powerful weapon in the form of information thermodynamics. The next step is to translate this theoretical framework into a form that can be applied to the understanding of biological phenomena, and to translate this into experiments. The dynamism between the extremes of biology and physics, experiment and theory, is perhaps the most exciting aspect of the boundary field of biophysics.

The title "Information Physics of Life" is the name of a new academic research area in which the author serves as a representative. Associate Professor Sousuke Ito (Universal Biology Institute), Associate Professor Kyogo Kawaguchi (Institute for Physics of Intelligence), and Associate Professor Kazumasa Takeuchi (Department of Physics) are the members of this project at the Graduate School of Science. In addition, Professor Sotaro Kamimura (Department of Biological Sciences) and Professor Hideo Higuchi (Department of Physics) are experts in single molecule measurements of protein molecules.


The Rigaku-bu News, November 2023

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