Out of the cell
Researchers at the RUB and from Taiwan discover energy supply for protein secretion
Journal of Biological Chemistry: mechanism of bacterial transport system published
Protein arsenal for many purposes
Bacteria use secreted proteins to make nutrients available, to fend off competitors and to infect human, animal or plant host cells. “Agrobacterium tumefaciens is a fascinating bacterium. It can genetically modify plants and stimulate tumour formation”, says Narberhaus. Five bacterial secretion systems have been known for a long time. The type VI system was only discovered a few years ago. Among other things, it transports the protein Hcp through two membranes into the environment – for what purpose is, as yet, unclear. The question of how the export of Hcp is driven was also unanswered. This is precisely what the German-Taiwanese team has now revealed.
Membrane protein TssM: the driver of the protein export
Narberhaus and his colleagues have shown that two proteins in the cell membrane of the bacteria, called TssL and TssM, are responsible for the export of Hcp. The molecule ATP, a cellular energy store, serves as fuel for the transport process. The membrane protein TssM binds the energy supplier ATP, thereby changing its own structure and splitting the ATP. The energy thus released allows the associated membrane protein TssL to bind its cargo (Hcp) so that a tripartite complex of TssM, TssL and Hcp is formed. Hcp only passes from the bacterial cell into the environment when this complex forms.
Successful cooperation between Bochum und Taiwan
“Large membrane proteins such as TssM are difficult to study biochemically. Our colleagues in Taiwan have done a great job” Prof. Narberhaus explains. “It will now be particularly interesting to explore the biological significance of the system.” The analyses of ATP splitting, also called hydrolysis, were established in Prof. Narberhaus’s laboratory by the doctoral student Lay-Sun Ma during a research visit. “Because of the participation in the Collaborative Research Centre SFB 642 ‘GTP- and ATP-dependent membrane processes’, we are able to offer ideal conditions for working with ATP-dependent proteins” the RUB-biologist explains. This is the second time that the DAAD has funded the cooperation between the laboratories of Franz Narberhaus and Erh-Min Lai. The successful cooperation is also to continue in the future. “It is bound to last for many years”, the Bochum researcher is convinced. The next exchange of doctoral students is planned for autumn.
L.-S. Ma, F. Narberhaus, E.-M. Lai (2012): IcmF family protein TssM exhibits ATPase activity and energizes type VI secretion, Journal of Biological Chemistry, doi: 10.1074/jbc.M111.301630