Primary structure alignments. Deduced amino acid sequence alignment of the putative cyanobacterial (green letters) and the E. coli (black letters) hydrogenase maturating endopeptidases. The top row indicates secondary structure features (H: alpha helix, S: beta sheet), which were extracted from the crystal structure of E. coli HydD  using the software tool DSSP . The conserved nickel coordinating amino acid residues are shaded yellow. The sequences are annotated with the (suggested) protein name plus the organism identification: PCC6803: Synechocystis PCC 6803, PCC7120: Anabaena PCC 7120, PCC73102: Nostoc punctiforme ATCC 29133/PCC 73102, PCC6301: Synechococcus PCC 6301, PCC7002: Synechococcus PCC 7002, Ecoli: Escherichia coli.