Comparisons of the catalytic domains of human Aurora-A, Aurora-B and Aurora-C kinases. A. Crystal structure of the catalytic domain of Human Aurora kinase with an adenosine molecule shown in the binding pocket (PDB ID 1muoA) . Residues lining the active site are colored purple when invariant and red when variant. B, Multiple sequence alignment of Auroras. Using the same color scheme as the structure in panel A, residues identified to be lining the active site are identified with invariant residues among all three Auroras marked with an asterisk. Of the 26 residues lining the active site, only three vary among the different human Aurora kinases; Leu215, Thr217 and R220 (numbering and residue identity based on Aurora-A), and all of this variation was found in Aurora-A.