Figure 1.

Working model of substrate recognition and discrimination by the chaperone domains of Clp proteins and Lon protease. The SSD subdomain of the ATPase domain or component binds appropriate substrates by recognizing motifs near the C or N terminus of substrates. Perhaps the strength and fidelity of the binding are increased by the presence of secondary binding sites also located in the ATPase domain. Conformational changes associated with ATP binding and/or hydrolysis promote either protein remodeling and reactivation or protein unfolding and translocation to the proteolytic component.