Putative Type V Secretion System Autotransporter Specific to Strain Paris

L. pneumophila strain Paris encodes a specific protein showing the typical structure of type V secretion systems. It contains three major domains: an N-terminal leader peptide for secretion across the inner membrane, a C-terminal domain that forms a pore in the outer membrane and processes the passenger domain to the cell surface (Desvaux et al. 2004). The passenger domain exposed to the cell surface usually confers on the protein a function in cell-cell aggregation. Consistent with this, the passenger domain of L. pneumophila is composed of hemagglutinin repeats similar to those ofthe Escherichia coli autotransporters AIDA-I and Ag43 (Benz and Schmidt 1992; Klemm et al. 2004). The L.pneumophila type V secretion system may thus mediate adherence to mammalian cells and/or autoaggregation during biofilm formation. However, the RGD (Arg-Gly-Asp) interaction motif present in AIDA-I and Ag43 lacks the L. pneumophila autotransporter. The presence of many remnants of insertion sequences upstream of this autotransporter, as well as its G+C content of 41% - which is higher than the genome average G+C content of 38% - suggest acquisition through horizontal gene transfer (Fig. 15.1).

Fig. 15.1 Chromosomal region containing the L. pneumophila Paris-specific autotransporter and comparison with strains Lens and Philadelphia 1. The black curve indicates variations in G+C content along this region in strain Paris. Homologous genes in the three strains are indicated by the same color code.

Fig. 15.1 Chromosomal region containing the L. pneumophila Paris-specific autotransporter and comparison with strains Lens and Philadelphia 1. The black curve indicates variations in G+C content along this region in strain Paris. Homologous genes in the three strains are indicated by the same color code.

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