3-methyl-2-oxobutanoate + CoA + 2 oxidized [2Fe-2S]-[ferredoxin] = 2-methylpropanoyl-CoA + CO2 + H(+) + 2 reduced [2Fe-2S]-[ferredoxin] Binds 2 [4Fe-4S] clusters. Heterotrimer of the VorA, VorB and VorC subunits.