Walt Whitman and his French critics

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Biological Roles of the Podospora anserina Mitochondrial Lon Protease and the Importance of Its N-Domain

Mitochondria have their own ATP-dependent proteases that maintain the functional state of the organelle. All multicellular eukaryotes, including filamentous fungi, possess the same set of mitochondrial proteases, unlike in unicellular yeasts, where ClpXP, one of the two matricial proteases, is absent. Despite the presence of ClpXP in the filamentous fungus Podospora anserina, deletion of the gene encoding the other matricial protease, PaLon1, leads to lethality at high and low temperatures, indicating that PaLON1 plays a main role in protein quality control. Under normal physiological conditions, the PaLon1 deletion is viable but decreases life span. PaLon1 deletion also leads to defects in two steps during development, ascospore germination and sexual reproduction, which suggests that PaLON1 ensures important regulatory functions during fungal development. Mitochondrial Lon proteases are composed of a central ATPase domain flanked by a large non-catalytic N-domain and a C-terminal protease domain. We found that three mutations in the N-domain of PaLON1 affected fungal life cycle, PaLON1 protein expression and mitochondrial proteolytic activity, which reveals the functional importance of the N-domain of the mitochondrial Lon protease. All PaLon1 mutations affected the C-terminal part of the N-domain. Considering that the C-terminal part is predicted to have an α helical arrangement in which the number, length and position of the helices are conserved with the solved structure of its bacterial homologs, we propose that this all-helical structure participates in Lon substrate interaction

PEROXYSOMES ET MITOCHONDRIES (DIFFERENCIATION CELLULAIRE ET REGULATION RETROGRADE CHEZ PODOSPORA ANSERINA)

LE ROLE QUE PEUVENT JOUER LES ORGANITES CELLULAIRES, EN PARTICULIER LES PEROXYSOMES ET LES MITOCHONDRIES, DANS LE DEVENIR CELLULAIRE EST ASSEZ PEU CONNU. L'ETUDE DES MUTANTS PEX2 (CAR1), CHEZ LE CHAMPIGNON FILAMENTEUX PODOSPORA ANSERINA AVAIT, DANS UN PREMIER TEMPS, SUGGERE QUE LES PEROXYSOMES POURRAIENT JOUER UN ROLE ESSENTIEL DANS LA DIFFERENCIATION. EN EFFET, CES MUTANTS, DEPOURVUS DE PEROXYSOMES ET INCAPABLES DE CROITRE SUR UN MILIEU CONTENANT DE L'ACIDE OLEIQUE COMME SEULE SOURCE DE CARBONE, SONT EGALEMENT INCAPABLES D'EFFECTUER LA TRANSITION ENTRE L'ETAT MITOTIQUE ET L'ETAT MEIOTIQUE. AFIN DE CONFIRMER LE LIEN ENTRE LES PEROXYSOMES ET LA DIFFERENCIATION, DES SUPPRESSEURS METABOLIQUES DES MUTANTS PEX2 ONT ETE RECHERCHES. SOIXANTE TROIS SUPPRESSEURS EXTRAGENIQUES, AFFECTANT SIX GENES (SUO), ONT AINSI PU ETRE ISOLES. ILS SUPPRIMENT TOUS LE DEFAUT DE CROISSANCE DES MUTANTS PEX2, MAIS AUCUN NE SUPPRIME COMPLETEMENT LEUR DEFAUT DE DIFFERENCIATION. LEURS PROPRIETES PHENOTYPIQUES SUGGERENT QUE DIFFERENTS MECANISMES SONT MIS EN PLACE POUR CES SUPPRESSIONS. JE ME SUIS PARTICULIEREMENT INTERESSEE AU GENE SUO4, LE SEUL DONT DES MUTATIONS, EN CONTEXTE PEX2 +, ENTRAINENT UN DEFAUT SEXUE : LES MUTANTS SUO4 SONT PRINCIPALEMENT BLOQUES AU STADE DIFFUS, PROPHASE DE PREMIERE DIVISION DE MEIOSE. CE GENE A ETE CLONE, IL CODE LA CITRATE SYNTHASE MITOCHONDRIALE (CIT1). CES MUTANTS SOULEVENT TROIS QUESTIONS MAJEURES. COMMENT PEUVENT-ILS ETRE VIABLES ? COMMENT LES MUTATIONS SUPPRIMENT-ELLES LES DEFAUTS DES MUTANTS PEX2 ET ENFIN POURQUOI ONT-ELLES DES EFFETS SUR LA REPRODUCTION SEXUEE ? LES ANALYSES PHYSIOLOGIQUES ET BIOCHIMIQUES SUGGERENT L'EXISTENCE D'UN MECANISME DE COMMUNICATION ENTRE LES MITOCHONDRIES ET LES PEROXYSOMES RESSEMBLANT A CELUI IDENTIFIE CHEZ LA LEVURE : LA REGULATION RETROGRADE. D'AUTRE PART, CETTE ETUDE A EGALEMENT PERMIS D'IDENTIFIER LES PREMIERS MUTANTS BLOQUES AU STADE DIFFUS NOUS CONDUISANT A PROPOSER UN ROLE CLE DE CE STADE CHEZ LES EUCARYOTES.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

The mitochondrial PaLON1 protein.

<p>(A) Schematic representation of the PaLON1 protein outlining the three domains present in both prokaryotes and eukaryotes. The N-domain, which is the most divergent domain between Lon proteins, is followed by the highly conserved ATPase and protease domains. Within the N-domain, the most conserved region is within the C-terminal part (hatched). The line referring to residues 382 to 619 indicates the part of the protein presented in (B). Diamond (S423L), point (L430P), and inverted triangles (Δ514–567) mark changes induced by <i>PaLon1-31</i>, <i>PaLon1-1</i> and <i>PaLon1-f</i>, respectively. (B). Primary sequence and secondary structure of the C-terminal part of the N-domain of <i>B. subtilis</i>, <i>E. coli,</i> and <i>P. anserina</i> Lon proteases. Sequences were aligned using the Clustal W program. Conserved amino acids are boxed in black (identical) and gray (similar). For the <i>P. anserina</i> sequence (PODAN), changes induced by <i>PaLon1</i> mutations are represented by the same symbols as in (A). The GenBank accession numbers for <i>B. subtilis</i> (BACSU) and <i>E. coli</i> (ESCCO) proteins are CAA99540.1 and AAC36871.1, respectively. The Walker A motif of the central ATPase domain is boxed and begins at position 607, 356, and 354 in <i>P. anserina</i>, <i>E. coli</i> and <i>B. subtilis</i> proteins, respectively. The predicted consensus secondary structure of the PaLON1 region was determined on the <a href="mailto:NPS@" target="_blank">NPS@</a> Web server <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038138#pone.0038138-Combet1" target="_blank">[42]</a> using a combination of available methods. For the same region, the secondary structure information available for <i>E. coli</i> and <i>B. subtilis</i> proteins ends at residue 245 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038138#pone.0038138-Li2" target="_blank">[32]</a> or contains a gap of 36 amino acids (dotted line), respectively <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038138#pone.0038138-Duman1" target="_blank">[33]</a>. For the <i>B. subtilis</i> protein, structure information was not available after the last α helix just before the Walker A motif. Secondary structures are indicated above each sequence as follows: lines, α helices; c letter, random coil (no secondary structure); and question mark (?), ambiguous state.</p