Fig. 4

Comparison of the structures obtained in this study with those published from other sources. a–c illustrate the fitting of ligands into the density maps of the three hABCC4 complexes we obtained. The density coverage of PGE₂ is relatively complete. In contrast, certain regions of MTX and cAMP exhibit poorer density coverage, indicating that the binding flexibility of these two ligands is greater than that of PGE₂. d, e compare the MTX-bound structure we obtained (9KRM) with the previously published structure (8BWP). The density distributions of the MTX ligands in both structures are similar. However, in 9KRM, the ligand density in the W995-R998 region is continuous, suggesting that the sparse and dispersed density in this region may belong to MTX and that MTX exhibits high binding flexibility in this area. f, g compare the PGE₂-bound structure we obtained (9KRN) with the previously published structure (8BWR). The density distributions of PGE₂ in 9KRN and 8BWR are consistent and continuous, indicating low binding flexibility of the ligand