Insight on flavinylation and functioning factor in Type B succinate dehydrogenase from Gram-positive bacteria

Succinate dehydrogenase (SDH), a multisubunit complex enzyme, catalyzes the oxidation of succinate to fumarate, coupled with quinone reduction. Maturation of each subunit and assembly of the complex is essential. However, little is known about the maturation mechanisms of SDH in Gram-positive bacteria. To elucidate the maturation of Type B SDH in Gram-positive bacteria, we heterologously expressed 3 SDH from Bacillus subtilis, Corynebacterium glutamicum, and Pelotomaculum thermopropionicum in Escherichia coli. The covalent binding of flavin adenine dinucleotide (FAD) at these SDH flavoprotein subunits was observed in heterologous expression as a complex. Their flavinylation was enhanced by the presence of the iron-sulfur subunit and fumarate. In contrast, the iron-sulfur subunit of heterologously expressed SDH without SDH activity showed no iron-sulfur clusters. These results suggest that during maturation of SDH, flavinylation is achieved by the complex and that other factors are required for the iron-sulfur cluster maturation.