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Shaking up a protein's tangled world.

There's violence in the microscopic world of proteins. The evidence -- continuously on display in the human body and other living systems -- is in the vibrations that surge through a myoglobin molecule when the bond between the molecule's iron-containing group and an attached carbon monoxide or oxygen molecule is broken. The stress created by the original bond is released, and the protein "relaxes" by sending quakelike waves along the molecule's convoluted twists and turns. In the human body, myoglobin, located in muscle, serves as a reserve supply of oxygen.

On its scale, "a proteinquake is far more violent than an earthquake," says Erramilli Shyamsunder of the University of Illinois at Urbana-Champaign. "The energy released is of the same order of magnitude as the total energy required to completely denature a protein."

But even more interesting to researchers is the way in which the energy involved is released. In the August PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES, the Illinois group, led by Hans Frauenfelder, proposes a new model suggesting that proteins behave a lot like glass or the earth. The vibrations appear in distinct stages, starting with small, rapid, local oscillations that evolve into larger but slower wiggles that wander over the entire molecule. The existence of this hierarchy of vibrations also means that a protein molecule doesn't lose its excess energy as quickly as a simpler mechanism would allow.

The similarities between earthquakes, glass vibrations and protein motions are quite remarkable, says Frauenfelder. "It gives us a concept that allows us to look at proteins in a more unified way," he says. "It's clear that the same phenomenon has to happen in essentially every protein reaction in some way."

In the Illinois experiments, a laser flash initially breaks the bonds between myoglobin's iron group and a carbon monoxide molecule. The researchers monitor the vibrations by observing changes over time at various temperatures in the intensity of several spectroscopic "markers." These markers are sensitive to small changes in the molecule's structure and reflect what's happening in the protein as a whole.

"Although it looks like an earthquake, we don't know exactly how the energy is dissipated," says Shyamsunder. "Right now, all we have are experimental data that chart the precise time course, temperature course and decay rate of the proteinquake. We don't have as yet a microscopic picture, just guesses about where the vibrations are occurring."

An equally compelling question is why a protein would behave like a glass. "Maybe the purpose is to keep the energy available locally longer so that it can be used for other biological work," says Shyamsunder, "but we have no experimental evidence for that."

The Illinois model may also lead to a fruitful collaboration between glass and protein specialists. "We hope it goes in both ways," says Frauenfelder. "They can help us and we can help them."

"The key question is whether or not the behavior of proteins can in fact be treated as a glasslike behavior," says usseau of AT&T Bell Laboratories in Murray Hill, N.J. "Ultimately, you want to unravel the physics that governs proteins, and once you really understand that, you want to relate it to the biological properties of the molecules."
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Author:Peterson, Ivars
Publication:Science News
Date:Aug 17, 1985
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