(A) Alignment of the amino acid sequence of PSAT from Bacillus circulans spp. Alkalophilus (BCIR), Bacillus alcalophilus (BALC), Entamoeba histolytica (EHIS), and E coli (ECOL). Highlighted letters indicate active site residues that interact with the cofactor PLP (light grey) and Cl- ions (dark grey). The substitution of Pro201 (BCIR PSAT) to Ala195 (EhPSAT) in the loop region has been highlighted in blue. (B) Homology model of EhPSAT dimer visualized through UCSF chimera. The cofactor PLP present in the active site is represented in cyan color. The inset shows stacking of the cofactor PLP(cyan color) and the Trp101(brown color) at the active site.