Legionella pneumophila Mip: New Function for an Old Protein?

Abstract

The macrophage infectivity potentiator (Mip) protein of Legionella pneumophila is one of the most studied Legionella proteins and has long been known to promote virulence. Mip protein has been purified and shown to possess peptidyl-prolyl cis/trans isomerase (PPI-ase) activity. Comparison of primary structures and crystallographic studies shows that Mip proteins have an N-terminal and a C-terminal domain. Type II secretion is one of five protein secretion systems that can mediate the export of proteins across the gram-negative outer membrane into the extracellular milieu and/or into target cells, and the authors have shown that the type II protein secretion system of L. pneumophila is required for optimal replication in macrophages, amoebae, and mice. Interestingly, one of transposon mutants (previously designated NU247) proved to contain a single transposon insertion in the mip gene, suggesting, for the first time, that Mip might influence protein secretion. This chapter talks about the NU247 reproducibly that showed a 40 to 70% reduction in p-NPPC hydrolase activity in its culture supernatants in comparison to the wild-type strain 130b. Since Mip is highly conserved in the Legionella genus, and surface and secreted Mip-like proteins are present in other pathogenic microorganisms, Mip and Mip-like proteins might promote the secretion of other important effectors.