The iron-sulfur scaffold protein HCF101 unveils the complexity of organellar evolution in SAR, Haptista and Cryptista

Abstract Background Nbp35-like proteins (Nbp35, Cfd1, HCF101, Ind1, and AbpC) are P-loop NTPases that serve as components of iron-sulfur cluster (FeS) assembly machineries. In eukaryotes, Ind1 is present in mitochondria, its function associated with the FeS clusters subunits respiratory Complex I, Nbp35 Cfd1 cytosolic (CIA) pathway, HCF101 involved photosystem I plastids plants (chHCF101). The AbpC protein operates Bacteria Archaea. To date, cellular distribution these considered to be highly conserved only a few exceptions. Results We searched for genes all members family analyzed their targeting sequences. were predicted reside cytoplasm some exceptions localization mitochondria; Ind1was found was (chHCF101) photosynthetically active eukaryotes. Surprisingly, we second paralog Cryptista, Haptista, SAR predominantly target mitochondria (mHCF101), whereas appeared absent organisms. also identified exceptions, apicomplexans possess mHCF101 localize cytosol mitochondria. Our predictions experimentally confirmed selected representatives Apicomplexa ( Toxoplasma gondii ), Stramenopila Phaeodactylum tricornutum , Thalassiosira pseudonana Ciliophora Tetrahymena thermophila ) by tagging transgenic reporter. Phylogenetic analysis suggested chHCF101 evolved from common ancestral independently Nbp35/Cfd1 proteins. Interestingly, phylogenetic supports rather lateral gene transfer bacteria than acquisition being either α-proteobacterial or cyanobacterial endosymbionts. Conclusion searches across eukaryotic lineages revealed SAR, Cryptista mitochondrial HCF101. Because plastid known thus far, discovery explains confusion regarding presence organisms possibly lost secondary (e.g., ciliates, Cryptosporidium reduced nonphotosynthetic (apicomplexans).