Some bacteria are armed with a system that works like a crossbow and that allows them to eliminate other microbes with which they compete in their ecological niche. The teams of Eric Cascales, Christian Cambillau and Alain Roussel, and Rémi Fronzes, reveal the structure and way of assembly of a membrane complex anchoring and guiding his crossbow arrow to the target bacteria. This study is published in the journal Nature
. The article can be found here: struct-T6SS-membrane-complex-sm
In the environment or in the human body, the bacteria do not live alone. They are in contact with other bacterial populations, unicellular organisms or eukaryotic cells. To better colonize the environment, bacteria have developed mechanisms for collaboration, information exchange and nutrients, but also antagonistic mechanisms in order to eliminate other bacterial species and facilitate their access to resources. Among those involved to kill other bacteria, the most effective is the type VI secretion system (T6SS), that comprises a contractile structure that functions like a micro-crossbow. An arrow ending with a top covered with toxins is surrounded by a sheath acting as a spring whose contraction propels the arrow towards the target bacteria to kill her. This structure synthesized in the predatory cell is anchored to its membrane by a multiprotein membrane complex. In this new study, these researchers were able to define the precise assembly pathway of the membrane complex and get a picture of its structure by electron microscopy and by X-ray diffraction, determined by Van Son Nguyen
, an ex USTH Master in Pharmacological, Medical and Agronomical Biotechnology student of 2010-2012 course
. This work allowed to determine how this structure is assembled and what it looks like, but they also provide information about its way of functioning. Indeed, changes in the complex are observable when the crossbow is in action and it is now clear that this complex not only anchors the crossbow to the membrane of the predatory bacterium but also serves as gate for the passage of the arrow and prevents that it creates damages in the attacking cell. Figure legend
: View of the X-ray structure of a part of the T6SS complex formed by two proteins (TssJ and TssMct). Inset: detail of the TssJ/TssMct molecular interface. Right
: view of the T6SS core electron microscopy structure with the the X-ray structures fit into it (OM/IM: Outer/Inner membrane). Below: scheme of the T6SS cross-bow firing toxins. Reference
: Eric Durand#, Van Son Nguyen#, Abdelrahim Zoued#, Laureen Logger, Gérard Péhau-Arnaudet, Marie-Stéphanie Aschtgen, Silvia Spinelli, Aline Desmyter, Benjamin Bardiaux, Annick Dujeancourt, Alain Roussel, Christian Cambillau*, Eric Cascales* and Rémi Fronzes*. Biogenesis and structure of the bacterial Type VI secretion membrane core complex. Nature, 300 :555-560 [doi: 10.1038/nature14667] (2015). Nature is a British interdisciplinary scientific journal, first published on 4 November 1869. It was ranked the world's most cited scientific journal by the Science Edition of the 2010 Journal Citation Reports, is ascribed an impact factor of approximately 42.4, and is widely regarded as one of the few remaining academic journals that publishes original research across a wide range of scientific fields. Nature claims an online readership of about 3 million unique readers per month. The journal has a weekly circulation of around 53,000 but studies have concluded that on average a single copy is shared by as many as eight people.