Enzymatic characterization of the enteropathogenic Escherichia coli type III secretion ATPase EscN

Type III secretion is a transport mechanism by which bacteria secrete proteins across their cell envelope. This protein export pathway is used by two different bacterial nanomachines: the flagellum and the injectisome. An indispensable component of these secretion systems is an ATPase similar to the F-1-ATPase beta subunit. Here we characterize EscN, an enteropathogenic Escherichia coli type III ATPase. A recombinant version of EscN, which was fully functional in complementation tests, was purified to homogeneity. Our results demonstrate that EscN is a Mg2+-dependent ATPase (k(cat) 0.35 s(-1)). We also define optimal conditions for the hydrolysis reaction. EscN displays protein concentration-dependent activity, suggesting that the specific activity changes with the oligomeric state of the protein. The presence of active oligomers was revealed by size exclusion chromatography and native gel electrophoresis. (C) 2007 Elsevier Inc. All rights reserved.