FIGURE 3. LepB interacts with Rab1–GTP and disrupts secretory transport in mammalian cells.

a, Ectopically produced LepB protein was localized in CHO FcRII cells using a LepB-specific antibody. Fluorescence micrographs show that LepB co-localized with GTP-locked Rab1(Q70L), but did not co-localize with wild-type Rab1 protein. b, Secretion of an alkaline phosphatase reporter protein was measured in HEK293 cells producing yellow fluorescent protein (YFP), the L. pneumophila RalF protein fused to GFP (GFP–RalF) as a positive control or LepB. The relative percentage of alkaline phosphatase protein in the tissue culture medium was determined, and is shown as the percentage in tested cells relative to the percentage in control cells producing YFP. Values are the average calculated from three independent assay wells  standard deviation, and show that both GFP–RalF and LepB interfered with alkaline phosphatase secretion significantly, as determined by unpaired two-tailed Student's t-test (asterisk, P < 0.001).