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ePaper created 2013-02-01, 09:35:07 | version 1.24.0
15 RESEARCH AT THE CENTRE | Simulation Proton migration along the cell membrane plays a key role in energy production in cells. With the aid of a simulation, Jülich researchers have now been able to demonstrate that there must be a previously unknown boundary layer in which protons move rapidly and efficiently. 3|2012 Research in Jülich Physicist Chao Zhang, PhD student at IAS-5, turned to physics to find out what hap- pens on the membrane. He is pictured here in front of a model of proton transport across the cell membrane. Protons in the Turbolayer an ab initio simulation of proton migra- tion, which means that he recreated the movement using the smallest particles. Simulations require an enormous com- putational effort, even for a few hundred atoms. With a total of 2000 atoms, the young Chinese scientist’s simulation is one of the biggest ever conducted in bio- physics throughout the world. This level of complexity posed a chal- lenge even to Jülich’s petaflop computer JUGENE. It took the computer 100 days to simulate proton transport for a few trillionths of a second. The results could E ach living cell is a power plant – and what is more, one that pro- duces its own fuel. Understanding how exactly this works is one of the fun- damental questions concerning re- searchers in the life sciences. Scientists know that the molecule adenosine triphosphate (ATP) acts as an energy source for all cells, and they also know that all cells produce ATP using the ener- gy resulting from the proton density gra- dient between the two sides of the cell membrane. But as far as the details go, a great deal remains to be explained. One example is the migration of pro- tons along the cell membrane. “The question is this: how are protons able to move in such a way that they reach the proton pumps regulating the gradient quickly?” says Chao Zhang. The Chinese physicist is pursuing a PhD under Prof. Paolo Carloni, head of the subinstitute for Computational Biomedicine (IAS-5), which has been part of Jülich’s Institute for Advanced Simulation since early 2012. IAS-5’s cooperation partners from Linz, Austria, succeeded in measuring the protons’ high mobility along the cell membrane. “They move as fast as if they were gliding through water, yet they re- main attached to the membrane all the while, which should in fact slow them down,” says Carloni. As the experimental researchers at Linz could not explain this result, Zhang made use of the opportunities offered by computer simulation. “I turned to phys- ics to find the explanation,” says the physicist. Taking quantum mechanical effects into consideration, he carried out change the way we understand energy production in cells. “There must be a second layer between the cell mem- brane and the water. The protons can travel along this layer as fast as if they were in water but still retain a hold on the membrane,” says Zhang. The previ- ously unknown layer is made up of inter- facial water, a type of water whose prox- imity to a surface gives it a special structure. How exactly this layer is formed is a question that will continue to occupy biophysicists in the years ahead. :: Institute for Advanced Simulation German Research School