Model of the active site of E. histolytica IscS and Thermotoga maritima NifS. The E. histolytica IscS putative three-dimensional structure (A) was deduced using the conceptually translated iscS sequence. The previously solved crystal structure of T. maritima NifS (B) [PDB accession number: 1EG5, ] was used as a template. The E. histolytica IscS sequence was aligned to the T. maritima NifS sequence using DeepView v3.7 [http://www.expasy.org/spdbv/, ] and manually improved based on an independent Clustal W alignment . Only residues involved in co-factor (PLP) and substrate (Cys) binding were selected in order to show the active site.