Alignment of structures of Hck and Csk protein kinases. Panel (a) and (b) show schematic drawings of the structures of Hck (PDB id 1ad5) and Csk (PDB id 1k9a) src kinases. The kinase domains, the SH2, and the SH3 domains are shown in orange, magenta, and yellow, respectively. (c) Superposition of both structures on the first rigid body, corresponding to the kinase domain (shown in in blue, 190 res, RMSD 0.90 Å). Hck kinase is shown in dark colors, Csk kinase in light colors. The substantially different positions of the SH2 and SH3 domains with respect to the kinase domain become visible. (d) Flexible superposition between the two structures. When superposed separately the three domains reveal a considerable level of structural conservation (1st rigid body: 190 atoms, RMSD 0.90 Å; 2nd rigid body: 81 atoms, RMSD 0.88 Å; 3rd rigid body: 55 atoms, RMSD 1.06 Å).