The swimming behaviour of Halobacterium cells controlled by a small network of interacting proteins
Halobacterium salinarum cells respond to light (phototaxis), nutrients, and noxious chemicals (chemotaxis) by swimming to those places of their natural habitat that provide the best living conditions available at the moment.
Sensory rhodopsin photoreceptors and receptors for chemical and physical stimuli feed into a core signal processing network composed of interacting cytoplasmic proteins which mediates signal integration, adaptation and motor response. Because the network is small and many molecular details are known, mechanistic questions related to receptor activation, functional cross-talk of receptors, or the biophysical chemistry of signal processing can be addressed at the single cell level.
A kinetic model of the signal processing network quantitatively predicts the cellular response to complex patterns of light stimulation, and the spontaneous behaviour of the cell. This model is continually refined to improve our systems level understanding and to incorporate more mechanistic details.
Sensing and response in Halobacterium is the first example where biophysicists have studied the structure and dynamics of a signaling network within the archaeal branch of life in detail. Amazingly, evolution has adapted a bacterial-type signal processing protein network to target an archaeal flagellar motor organelle, the archaellum.
Fig. 1 Simplified scheme of the core biochemical reactions that control the response of Halobacterium salinarum to light. Note that for simplicity, only one of many different receptors is shown.
- Jarrell, K. F., and S.-V. Albers. 2012. The archaellum: an old motility structure with a new name. Trends in Microbiology 20:307-312.
- Streif, S., W. F. Staudinger, W. Marwan and D. Oesterhelt. 2008. Flagellar Rotation in the Archaeon Halobacterium salinarum Depends on ATP. J.Mol.Biol. 384:1-8.
- Nutsch, T., D. Oesterhelt, E. D. Gilles, and W. Marwan. 2005. A Quantitative Model of the Switch Cycle of an Archaeal Flagellar Motor and its Sensory Control. Biophys. J. 89:2307-2323.
- Marwan, W., and D. Oesterhelt. 1999. Biochemical mechanisms of a simple behavioural response. Chemie in unserer Zeit 33:140-151.