In:
eLife, eLife Sciences Publications, Ltd, Vol. 2 ( 2013-07-30)
Abstract:
Humans and other animals can use the five senses—touch, taste, sight, smell, and hearing—to interpret the world around them. Single-celled organisms, however, must rely on molecular cues to understand their immediate surroundings. In particular, bacteria gather information about external conditions, including potential hosts nearby, by secreting protein sensors that can relay messages back to the cell. Bacteria export these sensors via secretion systems that enable the organism both to receive information about the environment and to invade a host cell. A total of seven separate secretion systems, known as types I–VII, have been identified. These different secretion systems handle distinct cargoes, allowing the bacterial cell to respond to a range of feedback from the external milieu. The type III secretion system, also known as the ‘injectisome’, is found in bacterial species that are enclosed by two membranes separated by a periplasmic space. The injectisome comprises different components that combine to form the basal body, which spans the inner and outer membranes, and a projection from the basal body, called the hollow needle, that mediates the export of cargo from a bacterium to its host or the local environment. The distance between the inner and outer membranes may vary across species or according to environmental conditions, so the basal body must be able to accommodate these changes. However, no mechanism has yet been established that might introduce such elasticity into the injectisome. Now, Kudryashev et al. have generated three-dimensional structures for the injectisomes of two species of bacteria, Shigella flexneri and Yersinia enterocolitica, and shown that the size of the basal body can fluctuate by up to 20%. Kudryashev et al. imaged whole injectisomes in these two species and found that the height of the basal body was proportional to the distance between the inner and outer membranes. To probe how this could occur, the properties of two proteins that are important components of the basal body were studied in greater detail. YscD, a protein that extends across the periplasmic space, was crystallized and its structure was then determined and used to develop a computer model to assess its compressibility: this model indicated that YscD could stretch or contract by up to 50% of its total length. The outer membrane component YscC also appeared elastic: when the protein was isolated and introduced into synthetic membranes, its length was reduced 30–40% relative to that observed in intact bacterial membranes. A further experiment confirmed the adaptability of the basal body: when the separation of the membranes was deliberately increased by placing bacteria in a high-salt medium, the basal body extended approximately 10% in length. Cumulatively, therefore, these experiments suggest that the in-built flexibility of the basal body of the injectisome allows bacteria to adjust to environmental changes while maintaining their sensory abilities and host-invasion potential.
Type of Medium:
Online Resource
ISSN:
2050-084X
DOI:
10.7554/eLife.00792.001
DOI:
10.7554/eLife.00792.002
DOI:
10.7554/eLife.00792.003
DOI:
10.7554/eLife.00792.004
DOI:
10.7554/eLife.00792.005
DOI:
10.7554/eLife.00792.006
DOI:
10.7554/eLife.00792.007
DOI:
10.7554/eLife.00792.008
DOI:
10.7554/eLife.00792.009
DOI:
10.7554/eLife.00792.010
DOI:
10.7554/eLife.00792.011
DOI:
10.7554/eLife.00792.012
DOI:
10.7554/eLife.00792.013
DOI:
10.7554/eLife.00792.014
DOI:
10.7554/eLife.00792.015
DOI:
10.7554/eLife.00792.016
DOI:
10.7554/eLife.00792.017
DOI:
10.7554/eLife.00792.018
Language:
English
Publisher:
eLife Sciences Publications, Ltd
Publication Date:
2013
detail.hit.zdb_id:
2687154-3
Permalink