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Bioinformatics of Mitochondria, …a top-down lecture… Martijn Huynen.

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Presentation on theme: "Bioinformatics of Mitochondria, …a top-down lecture… Martijn Huynen."— Presentation transcript:

1 Bioinformatics of Mitochondria, …a top-down lecture… Martijn Huynen

2 Urea cycle ATP production Citric acid cycle Heme synthesis Fatty acids oxidation Calcium signaling Heat generation Electrical signaling Apoptosis Coenzyme synthesis FeS clusters Central role of mitochondria in metabolism Alzheimer Parkinson Leber’s syndrome Leigh syndrome Friedreich’s ataxia Myopathies Diabetes

3 Endosymbiotic origin of mitochondria 16S Ribosomal RNA

4 Original rationales for the endosymbiosis 1: ATP ? (MCF family is strictly eukaryotic) 2: Oxygen sink ? (Andersson & Kurland) 3: H 2 ? (Martin & Muller) ATP O2O2 H2H2

5 Rickettsia Gain (Andersson & Kurland) and retargeting of proteins and retargeting of proteins Gene transfer Mitochondria Free-living, alpha-proteobacterial ancestor Gene loss

6 Alpha-proteobacterial proteins with the rest of the bacteria and archaea Eukaryotic + alpha-proteobacterial proteinsg in the same branch Identifying eukaryotic proteins with an alpha- proteobacterial origin based on their phylogeny

7 PHYLOME SELECTION OF HOMOLOGS, (Smith&Waterman) ALIGNMENTS AND TREE (Clustalx, Kimura+Dayhoff) GENOME GENOMES TREE SCANNING LIST Detecting eukaryotic genes of alpha-proteobacterial ancestry 6 alpha-proteobacteria 9 eukaryotes 56 Bacteria+Archaea 6 alpha-proteobacteria (22 500 genes)

8 Alpha-proteobacterial genes monophyletic with eukaryotic genes Non redundant orthologous groups: 630 446 speciesGenome size Selected %Groups Rickettsia prowazekii 83519623,5173 Rickettsia conorii 137423517,1192 Caulobacter crescentus 371866817,9480 Brucella melitensis 318857818,1403 Rhizobium loti 726096913,3 516 Rhizobium meliloti 615082113,3

9 False positives: Of the unrelated Deinococcus radiodurans the algorithm selects 1.3 %False positives: Of the unrelated Deinococcus radiodurans the algorithm selects 1.3 % False negatives: Of the 66 proteins encoded in the mitochondrial genome of Reclinomonas americana the procedure selects 49%False negatives: Of the 66 proteins encoded in the mitochondrial genome of Reclinomonas americana the procedure selects 49% Estimating false positives and false negatives, 630 orthologous groups appears a lower bound:

10 Saturation in the estimated size of the proto-mitochondrial proteome with an increasing number of sequenced alpha-proteobacterial genomes

11 Increasing the number of genomes leads to more accurate results: less false negatives, less false positives

12 -Catabolism of fatty acids, glycerol and amino acids -Some pathways are not mitochondrial in present day mitochondria Proto-mitochondrial metabolism non-mitoch.. mitochondrial not in yeast/human

13 Eric Schon, Methods Cell Biol 2001 (manually curated) Huh et al., Nature 2003 (green fluorescent genomics) 566 527 303 Proto-mitochondrial proteins in S.cerevisiae 10 59 35 293 Yeast mitochondrial proteome: Human mitochondrial proteome: Eric Schon, Methods Cell Biol 2001 755 508 The majority of the proto-mitochondrial proteome is not mitochondrial (anymore) 113 Proto-mitochondrial proteins in H.sapiens

14 t proteins loss gain re-targeting Ancestor Modern mitochondria From endosymbiont to organell, not only loss and gain of proteins but also “retargeting”: ~16% of the mitochondrial yeast proteins are of alpha- proteobacterial origin. ~65% of the alpha- proteobacteria derived set is not mitochondrial. Gabaldon and Huynen, Science 2003

15 Original rationales for the endosymbiosis Aerobic (…no hydrogenosomal eukaryotes have been published yet….)Aerobic (…no hydrogenosomal eukaryotes have been published yet….) Catabolizing lipids, glycerol and amino-acids, incomplete TCACatabolizing lipids, glycerol and amino-acids, incomplete TCA Benefit for host wider than either H 2, ATP or O 2 consumption: iron-sulfur clusters and a variety of metabolic pathwaysBenefit for host wider than either H 2, ATP or O 2 consumption: iron-sulfur clusters and a variety of metabolic pathways

16 From endosymbiont to organell: a turnover of protein in functional classes and an increase in specialization (middle columns: yeast, right columns: human) C: Energy conversion O: Protein turnover, chaperones J: Translation, Ribosomal structure F: Nucleotide metabolism G: Carbohydrate metabolism M: Cell envelope biogenesis COG functional classification Very low throughout: D: Cell division

17 Mitochondrial FtsZ in a chromophyte alga. Beech PL, Nheu T, Schultz T, Herbert S, Lithgow T, Gilson PR, McFadden GI Science 2000 A homolog of the bacterial cell division gene ftsZ was isolated from the alga Mallomonas splendens. The nuclear-encoded protein (MsFtsZ-mt) was closely related to FtsZs of the alpha-proteobacteria, possessed a mitochondrial targeting signal, and localized in a pattern consistent with a role in mitochondrial division. Although FtsZs are known to act in the division of chloroplasts, MsFtsZ-mt appears to be a mitochondrial FtsZ and may represent a mitochondrial division protein. Gene loss in the evolution of mitochondria

18 Kiefel BR Gilson PR Beech PL. Diverse eukaryotes have retained mitochondrial homologues of the bacterial division protein FtsZ. Protist. 2004 Mar;155(1):105-15. Mitochondrial fission requires the division of both the inner and outer mitochondrial membranes. Dynamin-related proteins operate in division of the outer membrane of probably all mitochondria, and also that of chloroplasts--organelles that have a bacterial origin like mitochondria. How the inner mitochondrial membrane divides is less well established. Homologues of the major bacterial division protein, FtsZ, are known to reside inside mitochondria of the chromophyte alga Mallomonas, a red alga, and the slime mould Dictyostelium discoideum, where these proteins are likely to act in division of the organelle. Mitochondrial FtsZ is, however, absent from the genomes of higher eukaryotes (animals, fungi, and plants), even though FtsZs are known to be essential for the division of probably all chloroplasts. To begin to understand why higher eukaryotes have lost mitochondrial FtsZ, we have sampled various diverse protists to determine which groups have retained the gene. Database searches and degenerate PCR uncovered genes for likely mitochondrial FtsZs from the glaucocystophyte Cyanophora paradoxa, the oomycete Phytophthora infestans, two haptophyte algae, and two diatoms--one being Thalassiosira pseudonana, the draft genome of which is now available. From Thalassiosira we also identified two chloroplast FtsZs, one of which appears to be undergoing a C-terminal shortening that may be common to many organellar FtsZs. Our data indicate that many protists still employ the FtsZ-based ancestral mitochondrial division mechanism, and that mitochondrial FtsZ has been lost numerous times in the evolution of eukaryotes.

19 -Complex I deficiency is a severe hereditary disease (patients < 5 year) without therapy For 60% of the patients no mutation is found in known CI genes -For 60% of the patients no mutation is found in known CI genes Zooming in on one mitochondrial complex, NADH:ubiquinone oxidoreductase (Complex I), and using gene loss for function prediction

20 Tracing the evolution of Complex I from 14 subunits in the Bacteria to 46 subunits in the Mammals by comparative genome analysis Bacteria: 14 subunits Algae: 30 Fungi: 37 Mammals: 46 Plants: 30

21 Issues in homology detection: that we do not detect sequence similarity does not mean that proteins are not homologous. Latest developments in homology detection: profile vs. profile searches The fungal ComplexI subunit NUVM is homologous to the Bovine subunit NB5M (B15), This homology can only be detected by profile vs. profile searches

22 Beyond Blastology, Cogoly: Phylogenies for orthology prediction The Complex I assembly protein CI30 has been duplicated in the Fungi. This can explain the presence of a CIA30-homolog in Complex I-less S.pombe

23 A methyltransferase derived from the alpha-proteobacterial ancestor of the mitochondria has a phylogenetic distribution identical to Complex I proteins, suggesting involvement of this protein in Complex I Mining the proto-mitochondrion for new Complex I proteins } Alpha-proteobacteria Gabaldon and Huynen, Bioinformatics 2005 } Fungi } Metazoa

24 Function prediction of Complex I proteins NUEM Cyanobacteria CIA30 is inserted in NueM in Cyanobacteria, suggesting an interaction between CIA30 and NueM in the eukaryotes as well. CIA30 Eukaryotes

25 Distribution of Complex I subunits among model species Experimentally verified Homolog present in genome, predicted gene Homolog present in genome, not predicted Absent from genome Plants,algae Fungi Mammals Insects Nematode Fish

26 Reconstructing Complex I evolution by mapping the variation onto a phylogenetic tree. After an initial “surge” in complexity (from 14 to 35 subunits in early eukaryotic evolution) new subunits have been gradually added and incidentally lost. Complex I loss is not always “complete”, S.cerevisiae and S.pombe have retained 1 and 3 proteins respectively Six of the eukaryotic Complex I proteins have been “recruited” from the alpha-proteobacteria

27 Tinkering in the eukaryotic evolution of Complex I: new subunits have been added “all over” the complex Gabaldon et al. (2005) J. Mol. Biol. See also Science (2005) 308, 167

28 Deconstructing protein complexes by tracing their evolution: The phylogenetic distribution of Complex I subunits suggests the presence of submodules and the functions of the individual proteins In eukaryotes evolution appears less “sub-modular” than in prokaryotes T. Friedrich’s model Huynen et al., FEBS lett. 2005

29 How about the origin of the peroxisome? Like mitochondria an organell involved in oxidative metabolism, but without a genome. Multiplication by fission has suggested an endosymbiotic origin.

30 Scenarios for the origin of the peroxisome and mitochondria B) A single origin followed by fission A) Independent endosymbiotic origins C) Retargeting of mitochondrial proteins Time

31 Alpha-proteobact Yeast (61 proteins)Rat (50 proteins) The yeast and rat peroxisomal proteomes contain a large fraction of proteins of alpha-proteobacterial origin (18-19%), besides a large fraction of proteins of eukaryotic origin (37-38%) unresolved

32 Most (90%) of the peroxisomal proteins of alpha- proteobacterial origin have paralogs in the mitochondria

33 The retargeting of mitochondrial proteins to the peroxisome has continued in recent evolution } Mitoch. Peroxisomal Signal peptide cleavage site Within the Cit1/2 protein family all proteins have a mitochondrial location (exp. data and/or predictions), expect Cit2p which is peroxisomal, and has lost the cleavage site (YS)

34 Tracing the evolution of the peroxisome: a continuous retargeting of proteins from various origins. (yellow = eukaryotic, green = alphaprot, red = actinomyc., blue = cyanobact.) The “ancestral peroxisome” was likely involved in  -oxidation, harboring Catalase to detoxify hydrogen peroxide.

35 Scenarios for the origin of the peroxisome and mitochondria B) A single origin followed by fission A) Independent endosymbiotic origins C) Retargeting of mitochondrial proteins Time

36 Studying evolution of organellar proteomes is not only interesting in itself, it also provides us with clues about the functions of proteins


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