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A Common Evolutionary Origin for Mitochondria and Hydrogenosomes (Symbiosis/Organelle/Anaerobic Protist) ELIZABETH T

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A Common Evolutionary Origin for Mitochondria and Hydrogenosomes (Symbiosis/Organelle/Anaerobic Protist) ELIZABETH T Proc. Natl. Acad. Sci. USA Vol. 93, pp. 9651-9656, September 1996 Evolution A common evolutionary origin for mitochondria and hydrogenosomes (symbiosis/organelle/anaerobic protist) ELIZABETH T. N. BuI*, PETER J. BRADLEYt, AND PATRICIA J. JOHNSONt#§ Departments of tMicrobiology and Immunology and *Anatomy and Cell Biology and tMolecular Biology Institute, University of California, Los Angeles, CA 90095 Communicated by Elizabeth F. Neufeld, University of California, Los Angeles, CA, June 21, 1996 (received for review May 12, 1996) ABSTRACT Trichomonads are among the earliest eu- hydrogenase, a marker enzyme of the hydrogenosome, nor do karyotes to diverge from the main line of eukaryotic descent. they produce molecular hydrogen. Pyruvate/ferredoxin oxi- Keeping with their ancient nature, these facultative anaerobic doreductase and hydrogenase are, in contrast, commonly protists lack two "hallmark" organelles found in most eu- found in anaerobic bacteria. Like mitochondria, hydrogeno- karyotes: mitochondria and peroxisomes. Trichomonads do, somes are bounded by a double membrane (15); however, the however, contain an unusual organelle involved in carbohy- inner membrane neither forms cristae nor contains detectable drate metabolism called the hydrogenosome. Like mitochon- cytochromes or cardiolipin as found in mitochondria (16, 17). dria, hydrogenosomes are double-membrane bounded or- Also, hydrogenosomes do not appear to contain FOF1 ATPase ganelles that produce ATP using pyruvate as the primary activity (18). On the other hand, ATP is produced in hydro- substrate. Hydrogenosomes are, however, markedly different genosomes via catalysis by succinyl CoA synthetase (19, 20), a from mitochondria as they lack DNA, cytochromes and the Krebs cycle enzyme that catalyzes the same reaction in hy- citric acid cycle. Instead, they contain enzymes typically found drogenosomes and mitochondria. in anaerobic bacteria and are capable of producing molecular To determine whether hydrogenosomes share a common hydrogen. We show here that hydrogenosomes contain heat origin with mitochondria or evolved independently of mito- shock proteins, Hsp7O, Hsp6O, and HsplO, with signature chondria, we have conducted biochemical and phylogenetic sequences that are conserved only in mitochondrial and analyses on heat shock proteins Hsp7O, Hsp6O, and HsplO of a-Gram-negative purple bacterial Hsps. Biochemical analysis the trichomonad, Trichomonas vaginalis. Phylogenetic analyses of hydrogenosomal Hsp6O shows that the mature protein using Hsp7O and Hsp60 have previously confirmed that mito- isolated from the organelle lacks a short, N-terminal se- chondria are endosymbiotic descendants from a-Gram- quence, similar to that observed for most nuclear-encoded negative purple bacteria (21, 22). The data reported here show mitochondrial matrix proteins. Moreover, phylogenetic anal- that a common endosymbiont gave rise to both mitochondria yses of hydrogenosomal Hsp7O, Hsp6O, and HsplO show that and hydrogenosomes. these proteins branch within a monophyletic group composed exclusively ofmitochondrial homologues. These data establish that mitochondria and hydrogenosomes have a common eu- MATERIALS AND METHODS bacterial ancestor and imply that the earliest-branching eu- Cells. Trichomonads were cultured, and whole cell extracts, karyotes contained the endosymbiont that gave rise to mito- cytosolic fractions, and purified hydrogenosomes were pre- chondria in higher eukaryotes. pared as described (19, 20). Isolation and Characterization of cDNA and Genomic The origin of the hydrogenosome, an enigmatic organelle Clones. T. vaginalis Hsp70 cDNA clone was isolated by screen- found exclusively in eukaryotes that lack mitochondria, has ing an expression library with polyclonal antisera made against been a topic of much debate (1-7). The hydrogenosome was purified hydrogenosomes, as described (23). A T. vaginalis first described (8, 9) and has been most extensively analyzed in Hsp70 genomic clone was isolated from a library constructed trichomonads (4). Hydrogenosome-like organelles have also in A Zap (19) with the cDNA as a probe following standard been identified in a broad phylogenetic range of organisms, procedures. Hsp6O and HsplO sequences were cloned by including rumen-dwelling ciliates (10-12) and fungi (13, 14) as polymerase chain reaction (PCR) with T vaginalis genomic well as free-living ciliates (3). In addition to lacking mitochon- DNA as template. Degenerate primers sets 5'-GC(TC)GG- dria, organisms that contain hydrogenosomes also share the (TC)GG(TC)CCAGG(TC)AAGGG(TC)ATG-3' and 5'-AC- feature of being facultative anaerobes. TGG(AG)ATCTT(AG)CG(AG)CC(AG)TG-3', and 5'-TC- Hydrogenosomes are the site of pyruvate fermentation and (ACT)GG(CT)AT(CT)GT(CT)AT(CT)CCA-3' and 5'-C- play a central role in carbohydrate metabolism in (AG)AC(AG)AT(AG)GC(AG)AG(AG)AT(AG)TC-3' were trichomonads. Within the organelle, pyruvate is broken down used to generate 330-bp and 273-bp fragments encoding parts to acetate, C02, and molecular hydrogen. This process is of Hsp6O and HsplO, respectively. The cloned PCR products coupled to ATP formation via substrate-level phosphoryla- were used as probes to obtain genomic clones containing the tion. Biochemical analyses of hydrogenosomes have revealed entire gene. The genes were sequenced according to the Sanger properties that are similar to those of mitochondria; however, method (Sequenase 2.0 kit; United States Biochemical). there are significant differences. For example, the enzyme that mediates decarboxylation of pyruvate in hydrogenosomes, Abbreviation: Hsp, heat shock protein pyruvate/ferredoxin oxidoreductase, is markedly different Data deposition: The sequences reported in this paper have been from its counterpart in mitochondria, the pyruvate dehydro- deposited in the GenBank data base [accession nos. U27231 and genase complex. Likewise, mitochondria- do- not possess a U27232 (Trichomonas vaginalis Hsp7O), U26966 (T. vaginalis Hsp6O), and U26965 (T. vaginalis HsplO)]. §To whom reprint requests should be addressed at: Department of The publication costs of this article were defrayed in part by page charge Microbiology and Immunology, 43-239 Center for the Health Sci- payment. This article must therefore be hereby marked "advertisement" in ences, University of California, Los Angeles, School of Medicine, Los accordance with 18 U.S.C. §1734 solely to indicate this fact. Angeles, CA 90095-1747. e-mail: [email protected]. 9651 Downloaded by guest on September 24, 2021 9652 Evolution: Bui et al. Proc. Natl. Acad. Sci. USA 93 (1996) Immunoblot Analysis. T. vaginalis whole cell extracts, cyto- A B solic fractions, and hydrogenosomes were isolated as described kDa kD)a (20). Lysates were prepared from untransformed BL21 cells 97- and from cells harboring the Hsp7O cDNA clone induced to 68-= _ express the clone in the presence of 1 mM isopropyl f-D- 68- 6-o Isp70 thiogalactoside, according to standard procedures. Protein (10 -............. Q.....,. gg) for each T. vaginalis subcellular fraction or Escherichia coli 43- and as lysate was analyzed by SDS/PAGE immunoblotting, 4 AJ described (20). Protein Purification and Amino Terminal Sequencing. T. 97- > ~ucL z vaginalis Hsp6O was isolated using ATP agarose by a modified Q of > E ;^ procedure (24). Purified hydrogenosomes (5 mg protein) o were resuspended in 1 mM EDTA, 0.2 mM phenylmethylsul- v: fonyl fluoride (PMSF), 50 ,tg of Na-(p-tosyl)lysine chlorom- ethyl ketone per ml, and 10 ,ug of leupeptin per ml, and C sonicated on ice five times for 10 sec, each with 1-min intervals kl)a until the solution was cleared. Lysed organelles were then 97- centrifuged at 2500 x g for 5 min at 4°C, and the supernatant 68- was recentrifuged at 8000 x g for 30 min at 4°C. The resulting Iauw 4inHsp6O supernatant was adjusted to 0.5 M KCl, 0.5 M NaCl, and 5 mM MgCl2. ATP-agarose (A2767; Sigma) was equilibrated with 43- buffer B (50 mM Tris, pH 8.0/1 mM EDTA/0.2 mM PMSF/ 0.5 M M mM and in the C KCl/0.5 NaCl/5 MgCl2) (24) proteins 3 >N at H supernatant were mixed with the agarose beads for 15 h 4°C, H H inverting end-to-end. The matrix was washed with 20 bed volumes of buffer B and eluted by increasing the [ATP] in buffer B from 5 to 15 mM. Proteins eluted at 10 mM ATP were FIG. 1. T. vaginalis Hsp7O and Hsp6O are localized in the hydro- subjected to 10% SDS/PAGE and immunoblot analysis using genosome. T. vaginalis subcellular fractions and bacterial lysates the Cyanobacteria (StressGen Biotechnologies, Sidney, Can- prepared from nontransformed E. coli strain BL21 and transformed E. ada) Hsp6O antisera to verify the presence of a cross-reacting coli expressing a trichomonad Hsp7O cDNA clone were size separated 60-kDa protein. The proteins were then concentrated, size- on 10% SDS/PAGE, electroblotted to nitrocellulose, and reacted with separated by 10% SDS/PAGE, and electroblotted onto a either antisera generated against total purified hydrogenosomes (A polyvinylidine difluoride filter (Bio-Rad) according to condi- and B) or antisera against Hsp6O from Cyanobacteria (StressGen Biotechnologies) (C). Tv WCE, T. vaginalis whole cell extract; Tv cyto, tions recommended by the manufacturer. The 60-kDa band T. vaginalis crude cytosolic fraction; Tv Hy, T. vaginalis purified was excised and subjected to microsequencing analysis by hydrogenosomes; Ec lysate, untransformed E. coli strain BL21 lysate; Edman degradation in the Biological Chemistry Microse- Hsp7O cDNA, lysate of E. coli expressing TvHsp7O cDNA clone. Size
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