Chemosensory Arrays

Chemosensory arrays are highly ordered, as you can best see from a bird’s-eye view, as in this lysed Salmonella typhimurium. 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.