According to the literature, structural domains which comprise this superfamily correspond to the structure of domain 3 in 4-hydroxy-3-methylbut-2-enyl diphosphate reductase, IspH (LytB). This iron-sulphur enzyme catalyses the final step of the methylerythritol phosphate (MEP) isoprenoid biosynthesis pathway which gives rise to the universal precursors of terpenes: isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). This pathway has been identified in many bacteria as well as algae and the chloroplasts of higher plants.

IspH is a monomeric enzyme comprised on 3-domains, all of which share a similar structure and, although there is no specific information related to the function of each domain, it seems like all of them are involved in the catalytic process.