Role of alpha-Helical Domains in Functioning of ATP-Dependent Lon Protease of Escherichia coli

摘要

Homooligomeric ATP-dependent LonA proteases are bifunctional enzymes belonging to the superfamily of AAA(+) proteins. Their subunits are formed by five successively connected domains, i.e., N-terminal (N), alpha-helical (HI(CC)), nucleotide-binding (NB), the second alpha-helical (H), and proteolytic (P) domains. The presence of the inserted HI(CC) domain determines the uniqueness of LonA proteases among the AAA(+) proteins. The role of the alpha-helical domains in the LonA protease functioning was studied with an example of E. coli Lon protease (Ec-Lon). The properties of the intact Ec-Lon and its mutant forms, i.e., Lon-R164A and Lon-R542A bearing the substituted arginine residues at the similar positions in the HI(CC) and H domains, were compared. The H domain was shown to play a crucial role in ATP hydrolysis and enzyme binding to the target protein. The HI(CC) domain is not decisive for the manifestation of the catalytic properties of the enzyme. However, it affects the functioning of Lon ATPase and peptidase sites and is involved in maintaining enzyme stability. The participation of the HI(CC) domain in the formation of three-dimensional structures of LonA proteases and/or their complexes with DNA is suggested.