Figure 7. Detailed Analysis of the Interactions between NKX2-5 and TBX5 on Nppa DNA.

(A) Schematic summary of protein-DNA interactions. Only direct contacts between protein and DNA molecules are labeled as no water molecules have been built.

(B) Structures of TBX5_TBD bound to DNA (yellow, PDB ID 2X6V) and unbound TBX5_TBD (brown; PDB ID 2X6U) superimposed on TBX5_TBD from NKX-TBX_linked (red) are shown in ribbon representation. The structure of NKX2-5_HD bound to DNA (cyan; PDB ID 3RHQ) superimposed on NKX2-5_HD from NKX-TBX_linked are shown in ribbon representation. DNA from the NKX-TBX_linked is shown in cartoon representation (grey).

(C) Structural comparison between DNA molecules from NKX-TBX_linked (red/grey/blue) and individually bound TBX5 (yellow), NKX2-5 (cyan), TBX3 (purple; PDB ID 1H6F), and idealized B-DNA of the Nppa promoter (orange). Lines indicate the central tracks of each individual DNA molecule.

(D) Close-up view of the interface between NKX2-5_HD (blue, cartoon) and TBX5_TBD (red, surface) highlighting the position of contributing and mutated residues.

(E) Graphs of filter-binding assays using radioactively labeled DNA in combination of different purified proteins (indicated below).

(F) Same as (E) using indicated point mutants. NKX2-5 M1 corresponds to NKX2-5_122-230 K157A; NKX2-5 M2 to NKX2-5_122-230 Q195A/R196A; NKX2-5 M3 to NKX2-5_122-230 K157A/Q195A/R196A; TBX5 M3 to TBX5_1-251 P139A/D140A/R150A/Q151A.

See also Figure S7.