Figure 3. Schematic illustration of chemoreceptor structure. The ‘classic’ chemoreceptor consists of an extracytoplasmic (periplasmic) ligand-binding domain and a transmembrane portion that connects to the cytoplasmic domain via a HAMP domain. The cytoplasmic domain contains the CheA/CheW binding domain and methylation sites that are substrate for CheR and CheB. See text for more details.