TMH4-7A and TMH10-7A mutants are expressed on the cell surface of HeLa cells and exhibit transport of most substrates, similar to WT P-gp. Cartoon representations of the TMH4 (A) and TMH10 (B) in green and cyan, respectively. Labeled residues shown as stick models were mutated to Ala to generate TMH4-7A and TMH10-7A mutant P-gps. HeLa-S3 cells were transduced with WT, TMH4-7A, and TMH10-7A mutant P-gp using the BacMam baculovirus system. After 24 h of incubation at 37 °C, cells were harvested and stained with human P-gp-specific monoclonal antibody MRK-16. (C) Cell surface expression data from flow-cytometric analysis. MRK-16 staining of cells with WT, TMH4-7A, and TMH10 mutant P-gp are indicated by black, green, and cyan curves, respectively. Isotype controls are in blue. The transport function of (D) TMH4-7A mutant P-gp and (E) TMH10-7A mutant P-gp for 15 tested fluorescent substrates. The transport efficacy of the mutants was calculated, and error bars indicate the SD of three independent experiments. The dotted line indicates the threshold (<30% compared to efflux by WT) taken as the lowest detectable level or no transport.