- A: few secondary structure elements
- X: Fe-S cluster binding domain in carbon monoxide dehydrogenase corrinoid/iron-sulfur protein gamma subunit
- H: Fe-S cluster binding domain in carbon monoxide dehydrogenase corrinoid/iron-sulfur protein gamma subunit
- T: Fe-S cluster binding domain in carbon monoxide dehydrogenase corrinoid/iron-sulfur protein gamma subunit
- F: FeS