Mitochondrial-type assembly of FeS centers in the hydrogenosomes of the amitochondriate eukaryote Trichomonas vaginalis Robert Sutak*, Pavel Dolezal*, Heather L. Fiumera†, Ivan Hrdy*, Andrew Dancis†, Maria Delgadillo-Correa‡, Patricia J. Johnson‡, Miklo´ sMu¨ ller§, and Jan Tachezy*¶ *Department of Parasitology, Faculty of Science, Charles University, Vinicna 7, 128 44 Prague 2, Czech Republic; †Division of Hematology and Oncology, Department of Medicine, University of Pennsylvania, 421 Curie Boulevard, Philadelphia, PA 19104; ‡Department of Microbiology, Immunology, and Molecular Genetics, University of California, 405 Hilgard Avenue, Los Angeles, CA 90095; and §The Rockefeller University, 1230 York Avenue, New York, NY 10021 Edited by William Trager, The Rockefeller University, New York, NY, and approved May 28, 2004 (received for review February 25, 2004) Mitochondria are the site of assembly of FeS centers of mitochon- dria (10, 11); however, this process has not yet been studied, to drial and cytosolic FeS proteins. Various microaerophilic or anaer- our knowledge, in hydrogenosomes. obic unicellular eukaryotes lack typical mitochondria (‘‘amito- Proteins involved in [FeS] cluster assembly within mitochondria chondriate’’ protists). In some of these organisms, a metabolically are homologs of bacterial proteins belonging to the iron–sulfur different organelle, the hydrogenosome, is found, which is cluster (ISC) assembly system (12). Isc orthologs have been iden- thought to derive from the same proteobacterial ancestor as tified in all eukaryotes, and their products are generally detected in mitochondria. Here, we show that hydrogenosomes of Trichomo- mitochondria (13–15); however, in some cell types, they are also nas vaginalis, a human genitourinary parasite, contain a key found in the cytosol and the nucleus (15–18). In Saccharomyces enzyme of FeS center biosynthesis, cysteine desulfurase (TviscS-2), cerevisiae, the mitochondrial ISC-like machinery plays an essential which is phylogenetically related to its mitochondrial homologs. role in the maturation of mitochondrial and extramitochondrial FeS Hydrogenosomes catalyze the enzymatic assembly and insertion of proteins (11). The role of the cytosolic and nuclear components FeS centers into apoproteins, as shown by the reconstruction of the remains to be clarified (15–18). In addition to the ISC system, two apoform of [2Fe-2S]ferredoxin and the incorporation of 35S from FeS biosynthetic systems occur in bacteria, the NIF (nitrogen labeled cysteine. Our results indicate that the biosynthesis of FeS fixation) system that is involved in the maturation of proteins of the proteins is performed by a homologous system in mitochondriate nitrogen-fixing machinery (19) and the SUF (mobilization of and amitochondriate eukaryotes and that this process is inherited sulfur) system (20). Homologs of suf genes occur also in plastid- from the proteobacterial ancestor of mitochondria. bearing eukaryotes where they are involved in the biosynthesis of FeS proteins of plastids (21). he human genitourinary parasite, Trichomonas vaginalis, and A model for [FeS] cluster formation in mitochondrion was proposed based on studies of yeast (22). The clusters are first Tother parabasalid protists display metabolic peculiarities. A ͞ striking deviation from ‘‘typical’’ eukaryotes is the lack of transiently assembled on Isu1p and or Isu2p proteins (homologs mitochondria and the presence of another organelle, the hydro- of bacterial IscU protein), which serve as a scaffold. S, as a protein associated persulfide, is provided from L-cysteine by genosome (1–4). This double-membrane-bound organelle dif- Ј fers from mitochondria in its lack of DNA (5) and many pyridoxal-5 -phosphate-dependent cysteine desulfurase Nfs1p (a metabolic characteristics (1, 6). Hydrogenosomes oxidize pyru- homolog of bacterial IscS protein). The source of Fe is not vate or malate to acetate and, in the absence of alternative known; however, frataxin has been suggested to be involved in Fe loading of the Isu proteins. The mitochondrial [2Fe- electron acceptors, to molecular hydrogen. Proteins of this ͞ pathway are pyruvate͞ferredoxin oxidoreductase, [2Fe- 2S]ferredoxin Yah1p and NADH ferredoxin reductase Arh1p 2S]ferredoxin and [Fe]hydrogenase, all of which contain FeS were suggested to provide electrons for a critical step in the centers. The oxidation of pyruvate and malate produces acetyl- process. Subsequently, the assembled [FeS] clusters are trans- CoA with the energy of the thioester bond used for substrate ferred to the catalytic centers of FeS proteins with the possible level phosphorylation of ADP to ATP (1). Hydrogenosomes do participation of a mitochondrial chaperone system (22, 23). not contain pyruvate dehydrogenase complex, tricarboxylic acid The same mechanism is assumed to function in other eu- cycle, cytochrome-mediated electron transport chain, cyto- karyotes (11). Detection of two genes in T. vaginalis coding for IscS homologs with putative hydrogenosomal import signals chrome oxidase, or F1F0-ATPase, which are characteristic com- ponents of classical mitochondria. The origin of hydrogenosomes suggested that FeS-center assembly in hydrogenosomes might be is much debated. The absence of DNA from parabasalid hydro- homologous to the mitochondrial system (24). The clustering of genosomes deprives us of the clues that an organellar genome the derived amino acid sequences with mitochondrial homologs could provide in resolving this question. Nevertheless, increasing in phylogenetic reconstructions strengthened this notion further tviscS-2 biochemical and phylogenetic evidence supports the notion that (24, 25). Here, we show that one of these genes ( )is expressed, translocated to hydrogenosomes, and involved in the hydrogenosomes derive from a common ancestor with typical biosynthesis of FeS proteins. Also, we show that in T. vaginalis, mitochondria (2, 3, 7). hydrogenosomes are the site of FeS center biosynthesis. These Similar to most mitochondrial proteins, hydrogenosomal pro- teins are coded by nuclear genes and posttranslationally trans- located into the organelles (8, 9). Protein import is directed by This paper was submitted directly (Track II) to the PNAS office. short targeting sequences at the N terminus of the nascent Data deposition: The sequences reported in this paper (GenBank accession nos. AF321005 proteins, and all examined soluble hydrogenosomal proteins and AF321006 for tviscS-1 and tviscS-2, respectively) have been updated to include the possess such sequences (2). It is reasonable to expect that the 5Ј-UTR sequences established in the present study. maturation of the FeS proteins is completed within the hydro- ¶To whom correspondence should be addressed. E-mail: [email protected]. genosomes by the insertion of FeS centers, as it is in mitochon- © 2004 by The National Academy of Sciences of the USA 10368–10373 ͉ PNAS ͉ July 13, 2004 ͉ vol. 101 ͉ no. 28 www.pnas.org͞cgi͞doi͞10.1073͞pnas.0401319101 Downloaded by guest on September 27, 2021 findings reveal a major functional similarity of typical mitochon- dria and parabasalid hydrogenosomes. Materials and Methods Organisms, Cultivation, and Cell Fractionation. T. vaginalis strain C-1:NIH (30001; American Type Culture Collection) was used throughout this study. The organisms were maintained in TYM medium with 10% heat-inactivated horse serum (pH 6.2) at 37°C. To study gene transcription under Fe-rich or Fe-restricted conditions, the medium was supplemented with 100 ␮M Fe- nitrilotriacetate or 50 ␮M 2,2-dipyridyl. S. cerevisiae YPH499 (204679; American Type Culture Collection) was grown in a rich medium containing 1% yeast extract, 2% peptone, 0.01% ade- nine sulfate, and 2% raffinose. Preparation of subcellular (cy- tosolic, large granule, and hydrogenosomal) fractions of T. vaginalis is described in Supporting Materials and Methods, which Fig. 1. Transcription of tviscS.(A) Conserved motifs of putative initiator is published as supporting information on the PNAS web site. elements (boxed letters) in the sequences of 5Ј regions preceding the TviscS Yeast mitochondria were obtained according to ref. 26. ORFs; asterisks indicate conceptual transcription start sites. (B) Synthesis of nascent mRNA. Cells maintained under Fe-rich (Feϩ) or Fe-restricted (FeϪ) RNA Synthesis in Permeabilized Cells and RT-PCR. Synthesis of conditions were permeabilized with lysolecithine and incubated in transcrip- 35 nascent mRNA was assessed in lysolecithin-permeabilized tion buffer containing [ P]UTP. The RNA was isolated and hybridized to ͞ trichomonad cells (27). The primers used for PCR amplification specific DNA probes immobilized on nitrocellulose. PFOR, pyruvate ferredoxin oxidoreductase. (C) RT-PCR using total RNA. ␤-tub., ␤-Tubulin. of specific DNA probes, as well as the conditions and primers used in RT-PCR, are given in Supporting Materials and Methods. ؅ by adding 5 mM EDTA. In controls, no organellar extract was Analysis of 5 -UTRs. Clones containing complete genes coding for added. Unincorporated radioactivity was removed by gel filtra- IscS-1 and IscS-2 were obtained by screening of a genomic DNA Ј tion. The samples were separated on nondenaturing 15% poly- EVOLUTION library, as described in ref. 24. The 5 -UTRs of the genes were acrylamide gels at 4°C. Radioactivity on the vacuum-dried gels sequenced by primer walking. was detected by phosphorimaging. In the time-course experi- ments, the bands corresponding to ferredoxin were cut out of the IscS Expression