7.2 Chemosensory Arrays Atlas of Bacterial and Archaeal Cell Structure Home
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Source: Cassidy et al. (2020) Structure: PDB 6S1K

Architecture

Here you see two of the basic units of a chemosensory array from Escherichia coli [68]. Each unit consists of a trimer of chemoreceptor dimers (a section of which is shown in orange), a kinase (in blue), and a coupling protein (in green). In the cell, these two units would further associate with four more into a rosette of six units, then with other rosettes, forming the extensive hexagonal array. Also keep in mind that these are just the stable components; additional proteins (including the response regulators) interact transiently with the receptors and kinases.

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Chemosensory Arrays

Chemosensory arrays are highly ordered, as you can best see from a bird’s-eye view, as in this lysed Salmonella typhimurium cell. Chemoreceptors come together as dimers, which in turn organize into trimers, which are further packed into the extensive hexagonal honeycombed array you see here. The hexagonal arrangement comes from the baseplate, where the kinases and coupling proteins bind into an ordered array (⇩). In what should be a familiar theme by now, organization provides a great benefit. Bacteria and archaea have a tremendous sense of smell, responding to as few as one or two molecules of an attractant, or many more. In fact, the range of chemical concentrations they can discriminate among extends over 5 orders of magnitude. But how can a single receptor transmit a signal efficiently? Perhaps it should share the message with its neighbors. The interlocking network of chemoreceptors enables just this kind of amplification; a target binding to one receptor may translate into activation of 36 adjacent receptors, enormously boosting the gain of the signal.

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