Alignment of selected regions of Euglena and trypanosome SdhB-n and SdhB-c with SdhB and FrdB homologs from other eukaryotes and bacteria. A. SdhB-n. B. SdhB-c. Euglenozoan SdhB-n and SdhB-c proteins were aligned with the same set of SdhB and FrdB proteins from other species. Alignments were edited to emphasize regions encompassing conserved Cys residues (denoted by *) responsible for co-ordinating Fe-S clusters. Numbering reflects corresponding amino acid residues in E. coli SdhB. Shading of columns indicates amino acid identity of 60% or higher. The letters a, b and c highlight particular residues in the alignment that are discussed in the text. Full organism names and database accession numbers are listed in 'Additional file 4: Accession numbers and allied information'.