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1st Einstein Lecture Dahlem: Hans Frauenfelder

Einstein, Brownian Motion, and Protein Dynamic

Apr 29, 2005

Just in time for the Einstein Year 2005 the opening event for the Einstein Lectures Dahlem took place on April 29. This high-ranking colloquium covers topics from all scientific areas that were influenced by Einstein’s thinking.

“During several events in the frame of the Einstein Year 2005 we will discuss the impact of scientific insight on modern society” said Dieter Lenzen, former president of Freie Universität Berlin. In the latest decades, the number of scientific inventions influencing the every-day-life literally exploded. Scientific results from Einstein’s discipline physics affect almost every area of life.

US physicist Hans Frauenfelder from Los Alamos National Laboratory held a lecture on “Einstein, Brownnian Motion, and Protein Dynamics” at the opening event.

The second of the three revolutionary papers by Einstein of 1905, treating Brownian motion, is relevant for the physics of proteins. Proteins are the workhorses of biology; they perform most functions in living systems. The structures of a large number of proteins has been determined, mainly by using X-ray diffraction. This technique owes a great deal to Max von Laue, who spent most of his life in Berlin and was a close friend of Einstein. Computers produce beautiful pictures of proteins. While these pictures show how proteins are constructed, they lead to the impression that proteins are rigid, like crystals. Proteins, however, can only function if they move or, in other words, fluctuate among different conformations. Here again is a connection to Einstein who was very much interested in fluctuations. Protein experiments prove the importance of fluctuations, and lead to a remarkable observation: Major protein motions follow the fluctuations in the solvent that surrounds the protein, but they can be much slower. This fact shows that proteins are not isolated machines, but work in close contact with their surroundings. But why are the protein motions slower than the solvent fluctuations? The solution of this puzzle is based on the fact that a given protein does not have a unique structure, but assumes a very large number of different conformations, called substates. The different substates are characterized by the energy landscape, a construct in a hyperspace. Here is where the analogy to Einstein’s Brownian motion comes in. To go from one state to another, say from a closed to an open gate that accesses the protein’s interior, the protein makes a random walk in the energy landscape. The gate opens not like a solid door, but through a very large number of small steps in the energy landscape. This fact explains why protein motions are slower than the solvent fluctuations. Thus Einstein’s insight is relevant also to the physics of proteins.

Hans Frauenfelder, born 1922, completed his doctorate in 1950 at ETH Zurich on surface physics. From 1952 to 1992, he was a member at the physics department of University of Illinois in Urbana-Champaign, consulting research on angular correlation, parity violation, the Mössbauer effect and nuclear physics. Since 1970, his field of interest moved to biological physics, the search for physical concepts and laws in biological systems, with a special focus on proteins. Frauenfelder is a member of the US National Academy of Sciences, the American Philosophical Society, the Royal Swedish Academy of Sciences and the Leopoldina.