Figure 1.

Flexible tails in chemotaxis receptors. Bacterial chemotaxis receptors such as Tsr and Tar are transmembrane homodimers with long α-helical coiled-coil domains. Sets of three dimers are associated at their cytoplasmic ends with downstream signaling proteins such as CheA and CheW. Carboxy-terminal regions of the receptors consist of about 30 amino acids with no obvious secondary structure and are thought to serve as flexible tethers for the methylating enzyme CheR and the demethylating enzyme CheB (not shown). Methylation sites are indicated by small circles. A typical cluster of receptors on the bacterial surface might contain several thousand such receptors in close proximity.