Chloroplast HCF101 is a scaffold protein for [4Fe-4S] cluster assembly

Serena Schwenkert , Daili J.A. Netz , Jeverson Frazzon , Antonio J Pierik , Eckhard Bill , Jeferson Gross , Roland Lill , Jörg Meurer (1)

1 Department Biologie I, Botanik

Oxygen evolving chloroplasts possess their own iron-sulfur cluster assembly proteins including members of the SUF and the NFU family. Recently, the chloroplast protein HCF101 (high chlorophyll fluorescence) has been shown to be essential for the accumulation of the membrane complex photosystem I and the soluble ferredoxin-thioredoxin reductases, both containing [4Fe-4S] clusters. The protein belongs to the FSC ([4Fe-4S]-cluster) superfamily of P-loop NTPases, several members of which play a crucial role in Fe/S cluster biosynthesis. Although the C-terminal Fe/S cluster binding site conserved in other members of the FSC family is not present in chloroplast HCF101 homologues, using Mössbauer and EPR spectroscopy, we provide evidence that HCF101 binds a [4Fe-4S] cluster. 55Fe incorporation studies of mitochondria-targeted HCF101 in S. cerevisiae confirmed the assembly of an Fe/S cluster in HCF101 in a Nfs1-dependent manner. Site-directed mutagenesis identified three HCF101-specific cysteine residues required for assembly and/or stability of the cluster. We further demonstrate that the reconstituted cluster is transiently bound and can be transferred from HCF101 to a [4Fe-4S] apoprotein. Together, our findings suggest that HCF101 may serve as a chloroplast scaffold protein that specifically assembles [4Fe-4S] clusters and transfers them to chloroplast membrane and soluble target proteins.

Mots clés: Life Sciences

Serena Schwenkert, Daili J.A. Netz, Jeverson Frazzon, Antonio J Pierik, Eckhard Bill, et al.. Chloroplast HCF101 is a scaffold protein for [4Fe-4S] cluster assembly. Biochemical Journal, 2009, 425 (1), pp.207-214. ⟨10.1042/BJ20091290⟩. ⟨hal-00479247⟩