Superposition of alanine racemase monomers from Gram-positive bacteria. (A) Cα atom traces of alanine racemases from G. stearothermophilus (yellow) , E. faecalis (green) , B. anthracis (blue) , S. lavendulae (red) , and S. pneumoniae (pink). The superposed N-terminal α/β barrel domains are oriented on the bottom of the picture and the C-terminal β-strand domains on the top. Spheres represent the three structurally equivalent residues used to measure the hinge angle in each structure. The double-headed arrow indicates the variation between hinge angles. The PLP-bound Lys residue from AlrSP is shown in black. (B) Superposed ribbon representations of the N-terminal domains from E. faecalis (green)  and S. pneumoniae (pink), with the most divergent regions colored orange.