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IUPUI researchers explain how proteins survive the immense heat they create



INDIANAPOLIS — How do some proteins survive the extreme heat generated when they catalyze reactions that can happen as many as a million times per second? Work by researchers from Indiana University-Purdue University Indianapolis and the University of California Berkeley published online Dec. 10 in Nature provides an answer.

 Proteins are essential to the human body, doing the bulk of the work within cells. Proteins are large molecules responsible for the structure, function and regulation of tissues and organs. Enzymes — special proteins that catalyze chemical reactions within cells — are critical to every bodily function from breathing to walking. Some enzymes produce a lot of heat per reaction — enough heat, in fact, that if that heat were to be injected in another protein, that protein would overheat and unfold. So, how do enzymes expel that heat without overheating and self-destructing?

 Steve Pressé, assistant professor of physics in the School of Science at IUPUI, led the study’s theoretical arm. He is co-corresponding author of the Nature study by Riedel et al. along with Howard Hughes Medical Institute investigator Carlos Bustamante of the University of California Berkeley, who led the experimental research arm of the study in close collaboration with Susan Marqusee, also of UC Berkeley.

 ”A critical goal in improving human health will be to understand how a protein recovers from a reaction and, ultimately, how to speed up its activity,” said Pressé, a biophysicist at IUPUI.

“We have discovered a key fact that explains how enzymes recover from a reaction: Enzymes dissipate heat by very rapidly accelerating immediately following the reaction. This finding has very deep implications regarding how heat flows in living systems.”

 To illustrate how this heat transfer appears to occur, Pressé refers to an observation made by Alexander Graham Bell in the 19th century, which lead to the discovery of the “photoacoustic effect”. Noting that metal — when exposed to sun and then to shade — emitted a ringing sound, Bell concluded that heat from light expanded the metal, which then contracted in the shade. In doing so, the metal sent audible pressure waves into the air. 

 Similarly, Pressé said, enzymes respond to the energy released during catalytic reactions by expanding and contracting, which in turn violently propels the enzyme and generates a pressure wave — the study authors call it a chemoacoustic wave  — because it is caused by the heat of a chemical reaction.   

 ”Think of proteins as stepping on landmines,” Pressé said. “We asked, ‘How does a protein avoid damage from the enormous amounts of heat released and not break apart?’ Now we have shown that they cope with this heat assault by pushing that energy outwards from the reaction site as chemoacoustic waves and propelling themselves away in the meanwhile.”

 The Pressé, Bustamante and Marqusee labs plan to continue investigating this puzzling “chemoacoustic effect” on a number of other proteins using a variety of experimental and theoretical methods.

 The Nature paper is titled “The Heat Released During Catalytic Turnover Enhances the Diffusion of an Enzyme.” In addition to Bustamante, Pressé and Marqusee authors are Konstantinos Tsekouras of IUPUI; as well as C. Riedel, R. Gabizon and K.M. Hamadani from UC Berkeley; and C.A.M. Wilson from Universidad de Chile.

 This research was supported in part by the National Institutes of Health, the U.S. Department of Energy and the National Science Foundation.

 About the School of Science

The School of Science at IUPUI is committed to excellence in teaching, research and service in the biological, physical, behavioral and mathematical sciences. The school is dedicated to being a leading resource for interdisciplinary research and science education in support of Indiana’s effort to expand and diversify its economy.