Site-directed mutagenesis studies of the amino acid residue at position 412 of Escherichia coli TolC which is required for the activity

The Escherichia coli ToIC acts as a channel-tunnel in the transport of molecules across the outer membrane. We previously showed that the region extending from the 50th to the 60th amino acid residues from the carboxy terminus is involved in the transport activity of ToIC. To clarify which amino acids are important to the activity, we mutated the gene coding these residues and examined the activity of the mutant ToICs. The results showed that leucine at position 412, the 60th amino acid residue from the carboxy terminal end, is important. Further mutational research on We residue suggested that ToIC required a nonpolar amino acid residue at position 412 to express its activity. (C) 2002 Elsevier Science Ltd. All rights reserved.