Fig 3. Highly flexible active site of SrLDC.

(A) Open and closed conformational changes of the active site of SrLDC. The SrLDC structures in the apo-form and complexed with PLP/cadaverine are superimposed and presented with cartoon diagrams. The AS-loop, the PS-loop, and the R-loop in the open and closed conformations are distinguished with different colors and labeled. The bound PLP and cadaverine are shown as stick models with salmon and yellow colors, respectively. (B) (C) Surface models of the open and closed conformations. The AS-loop, the PS-loop, and the R-loop in the closed (B) and open (C) conformations are presented with surface models with the same color scheme as in (A). (D) (E) Stabilization mode of the PS-loop and the R-loop. The PS-loop and the R-loop in the closed (D) and open (E) conformations are presented with cartoon diagrams with the same color scheme as in (A). Side-chains involved in the stabilization of the PS-loop and the R-loop are shown as stick models. Main-chains involved in the stabilization of the PS-loop and the R-loop are shown as stick models and their side-chains are as line models. Hydrogen bonds are presented as red-colored dotted lines. (F) Superimposition of SrLDC structures in three different crystal forms. Four monomeric SrLDC structures in three different crystal forms are superimposed and presented as cartoon diagrams. The AS-loop, PS-loop, and the R-loop of four monomers are distinguished with different colors and labeled. (G) B-factor presentation of SrLDC structures in three different crystal forms. The crystal forms are labeled at the bottom of the figures. The AS-loop, PS-loop, and the R-loop are labeled.