Table 1.

FeS cluster substitutions observed in sequence databases

Species	Accession	Cluster, position	Substitution
M. barkeri	YP_305362	Proximal (4Fe4S)?, 1	Cys to Asp
G. metalloreducens	YP_006722286	Proximal (4Fe4S)?, 2	Cys to Asp
N. punctiforme	YP_001864093	Proximal (4Fe4S), 2	Cys to Asn
N. punctiforme	YP_001864093	Distal (4Fe4S), 1	His to Gln
N. punctiforme	YP_001864093	Medial (3Fe4S), 2	Pro to Lys*
D. baculatum	YP_003157302	Medial (4Fe4S), 2	Pro to Cys

Putative FeS cluster ligating residues deviating from the standard pattern seen among two-subunit [NiFe]-hydrogenases. Each substitution is represented by multiple members; only one representative example is listed. Question marks indicate FeS cluster assignments that have not been confirmed. Asterisk (“*”) indicates a substitution not investigated in this study. The final entry represents [NiFeSe] hydrogenases, which do feature a cysteine in lieu of a proline.