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uni'wissen 02-2015_ENG

Further Reading Shahapure, R. / Driessen, R. P. / Haurat, M. F. / Albers, S.-V. / Dame, R. T. (2014): The archaellum: A rotating type IV pilus. In: Molecular Micro- biology 91/4, pp. 716–723. Reindl, S. / Ghosh, A. / Williams, G.J. / Lassak, K. / Neiner, T. / Henche, A.L. /Albers, S.-V. / Tainer, J. A. (2013): Insights into FlaI functions in archaeal motor assembly and motility from structures, conformations, and genetics. In: Molecular Cell 49/6, pp. 1069–1082. Jarrell, K. F. / Albers, S.-V. (2012): The archaellum: An old structure with a new name. In: Trends in Microbiology 20/7, pp. 307–312. move in a way similar to bacteria with the help of filament-like structures.” These structures are whips made of protein filaments and work similarly to a propeller: A “motor” on the end anchored to the cell wall starts them rotating, enabling a swimming motion. It wasn’t until the 1980s that studies demonstrated that the movement appa- ratus of the archaea has an entirely different structure than that of bacteria. However, these studies assumed that the structure was a so-called flagellum like those of bacteria. From Flagellum to Archaellum The first indications that the structure allowing the archaea to move is different came from the field of genomics. While a bacterium’s flagellum needs up to 50 proteins to start the motor ena- bling it to reach its goal, Sulfolobus needs only seven proteins. Albers and her colleague Ken Jarrell from Queen’s University in Ontario, Canada, collected a large amount of data showing that an archaeon’s flagellum is fundamentally different from the complex structure of bacteria. The two decided to rule out potential confusion as to the name of the structures and published an article calling the archaeon’s flagellum an “achaellum” in 2012. Two years later, the name was added to standard microbiology textbooks. “We thus made it clear to students that these are two clearly distinguishable structures,” explains Albers, “flagellum for bacteria and archaellum for archaea.” The corresponding structure in eukaryotes is called a cilium. “All three are domain-specific and evolved independently of one another.” Another task of the fundamental research Albers is engaged in concerns determining the functions the various proteins in the unicellular archaellum are responsible for. What is certain is that several proteins remain inside the cell, while the motor protein in the cell wall helps them to coordinate the contact with the outside world by way of the thin, cord-like filament proteins outside of the cell. “This tiny, minimalistic motor structure is just as efficient and fast as the more complicated structure of the flagella,” says the microbiologist – she can imagine that what she describes as a “nanomachine” could also pro- vide inspiration for nanobiotechnology. There is already a candidate for the motor protein, which does not destroy the membrane of the cell wall despite its propeller-like rotation and holds the archaellum in place. “We also still need the pre- cise structure of the other subunits, and we do not yet know how the movement looks in detail.” This will involve genetically modifying individual elements, whose absence provides indications concerning their function. What Sulfolobus – in contrast to the halophilic (salt-loving) archaea – does not have due to its small size is the ability to react to an external stimulus and change its direction by initiating a so-called signal transduction cascade. “Bacteria can identify and head straight for substances that interest them – like a computer that ensures that the stimulus reaches the motor,” the researcher explains. Despite the fact that they have entirely different motors, halophilic archaea and bacteria use the same mechanism to link their movement structure to an external stimulus. “The archaea have adopted the system of bacteria and adapted it to their own motor.” In the end, when the researchers have explained the interplay between all of the elements, they plan to create a three-dimensional image of the entire archaellum. Prof. Dr. Sonja-Verena Albers was appointed to a chair in microbiology at the Institute of Biology II of the Univer- sity of Freiburg in 2014. Af- ter studying biology in Würzburg, she wrote her degree thesis at the Max Planck Institute of Biochem- istry in Martinsried. She earned her PhD at the Rijk- suniversiteit Groningen, Netherlands, and received a grant from the Dutch sci- ence organization NWO to establish her own research group. In 2008 she was ap- pointed Max Planck re- search group leader at the Max Planck Institute for Ter- restrial Microbiology, and in 2011 she completed her ha- bilitation at the University of Marburg. In 2012 Albers received a starting grant from the European Re- search Council to continue her research on the ar- chaellum. Photo: private 31