Targeting of GroEL to SecA on the cytoplasmic membrane of Escherichia coli

Chaperonin GroEL has been found to interact with isolated cytoplasmic membrane ofEscherichia coli . Interaction requires Mg ions, whereas MgATP inhibits, and inhibition is stronger in the presence of co-chaperonin GroES. “Heat-shock” of the membrane at 45°C destroys irreversibly its ability to bind GroEL. The binding of GroEL is characterized by saturation with a maximum of about 100 pmol GroEL bound per mg of total membrane protein, indicating a limited capacity and specificity of the membrane to bind GroEL. According to results of immunoblotting analysis and cleavable photoactivable cross-linking, a membrane target of GroEL is SecA, a protein known as a central component of the translocation machinery. Moreover, in some cases GroEL could modulate a cycle of association of SecA with the membrane by stimulating release of SecA from the membrane. A physiological role of targeting of GroEL in or close to the protein-conducting membrane apparatus is discussed.