Characterization of Mip proteins of Legionella pneumophila.

The Mip ('macrophage infectivity potentiator') protein of Legionella pneumophila has been shown to be an essential virulence factor, exhibiting peptidyl-prolyl cis/trans isomerase (PPIase) activity that can be inhibited by the immunosuppressant FK506. The cloning and sequencing of mip genes from three different L. pneumophila strains revealed a single amino acid substitution which did not affect the isomerase property of the enzyme. Mip proteins isolated from two wild-type L. pneumophila strains and from two corresponding Escherichia coli K-12 recombinant clones derived from these strains exhibited identical enzymatic properties and the precursor proteins are processed at identical cleavage sites. The mature Mip proteins exist in an oligomeric form. Site-directed mutagenesis demonstrated that a substitution of an Asp residue at position 142 by a Leu residue affects PPIase activity of Mip.