Frataxin as the Source of Ferrochelatase Activity in Plant Mitochondria

BUSI, MARIA VICTORIA; TERENZI, AGUSTINA; GOMEZ-CASATI, DIEGO FABIAN; ARMAS, ALEJANDRO MANUEL; PAGANI, MARIA AYELEN

Congreso; XLVIII Annual Meeting of Brazilian Biochemistry and Molecular Biology Society; 2019

Frataxin (FH) plays a key role in celular iron homeostasis of different organisms. It is engaged in several activities at the Fe-S cluster assembly machinery and it is also involved in heme biosynthesis. In plants, two genes encoding ferrochelatases (FC1 and FC2) catalyze the incorporation of iron into protoporphyrin IX in the last stage of heme synthesis in chloroplasts. Despite ferrochelatases are absent from other cell compartments, ferrochelatase activity has been observed in plant mitochondria.Here we analyze the possibility that frataxin acts as the iron donor to protoporphyrin IX for the synthesis of heme groups in plant mitochondria as an alternative to the regular chloroplastic pathway.We expressed and purified the proteins frataxin, AtNFS1, and AtISD11 to study their ability to form heme in vitro. The products in the reaction mix were analyzed by thin layer chromatography. Heme content and catalase activity were measured in AtNFS1 overexpressing and knockdown mutant Arabidopsis plants.Our findings show that frataxin catalyzes the formation of heme in vitro when it is incubated with iron and protoporphyrin IX. When frataxin is combined with AtNFS1 and AtISD11 the ferrochelatase activity is increased suggesting that a protein complex is formed that regulates the activity of both At NFS1 and frataxin. AtNFS1 overexpressing and mutant plants showed alterations in the heme content and in the catalase activity.These results suggest that frataxin could be the iron donor in the final step of heme synthesis in plant mitochondria, and constitutes an important advance in the elucidation of the mechanisms of heme synthesis in plants.