The crystal structure of tetrameric form Trpase of E. coli created by symmetry operation of single monomer. Molecule A is colored by domains; large domain is colored in blue and small domain in magenta. The other three monomers of the tetramer are colored in gray. The non-catalytic axis (vertical) and catalytic axis (horizontal) are shown as lines perpendicular to each other. Mutation sites of residue 74 (orange), residue 298 (red), and 330 (green) as well as the PLP molecule (cyane) are shown as CPK.