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087 - 104
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X-Bacteria, obligatory endosymbionts in the xD strain of Amoeba proteus, contain a macrophage infectivity potentiator (Mip)-like protein. We detected a 30-kDa Mip-like protein (Mipx) in X-bacteria by immunoblotting using an antibody against Mip of Legionella pneumophila as a probe. Using conserved nucleotide sequences from Legionella mip genes as primers, we obtained PCR products containing mip-like gene (mipx) from a genomic expression library of X-bacteria. We confirmed the presence of mipx in the genomic DNA of X-bacteria by Southern hybridization using a P-32-labeled PCR fragment as a probe. The mipx gene had a sequence identity of 79% and 74% with genes of Legionella micdadei and L. pneumophila, respectively. Mipx protein contained amino acids corresponding to the peptidyl-prolyl cis-trans isomerase (PPIase) activity region at its C-terminus. Recombinant Mipx protein produced by E. coli transformed with mipx exhibited the PPIase enzyme activity and the activity was inhibited by immunosuppressive drug, FK506. When X-bacteria were pretreated with FK506, X-bacteria's infectivity in amoebae was reduced to one-third that of the control group, and the results suggested that Mipx is involved in the initial infection of X-bacteria in amoebae.
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