Converts 2C-methyl-D-erythritol 2,4-cyclodiphosphate (ME-2,4cPP) into 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate. (2E)-4-hydroxy-3-methylbut-2-enyl diphosphate + H2O + 2 oxidized [2Fe-2S]-[ferredoxin] = 2-C-methyl-D-erythritol 2,4-cyclic diphosphate + H(+) + 2 reduced [2Fe-2S]-[ferredoxin] Binds 1 [4Fe-4S] cluster. Isoprenoid biosynthesis; isopentenyl diphosphate biosynthesis via DXP pathway; isopentenyl diphosphate from 1-deoxy-D-xylulose 5-phosphate: step 5/6. Belongs to the IspG family.