A stable sub-complex between GCP4, GCP5 and GCP6 promotes the assembly of γ-tubulin ring complexes.

γ-Tubulin is the main protein involved in the nucleation of microtubules in all eukaryotes. It forms two different complexes with proteins of the GCP family (γ-tubulin complex proteins): γ-tubulin small complexes (γTuSCs) that contain γ-tubulin, and GCPs 2 and 3; and γ-tubulin ring complexes (γTuRCs) that contain multiple γTuSCs in addition to GCPs 4, 5 and 6. Whereas the structure and assembly properties of γTuSCs have been intensively studied, little is known about the assembly of γTuRCs and the specific roles of GCPs 4, 5 and 6.

A yeast-based screening assay identifies repurposed drugs that suppress mitochondrial fusion and mtDNA maintenance defects.

Mitochondria continually move, fuse and divide, and these dynamics are essential for the proper function of the organelles. Indeed, the dynamic balance of fusion and fission of mitochondria determines their morphology and allows their immediate adaptation to energetic needs as well as preserving their integrity. As a consequence, mitochondrial fusion and fission dynamics and the proteins that control these processes, which are conserved from yeast to human, are essential, and their disturbances are associated with severe human disorders, including neurodegenerative diseases.

Assembly and regulation of γ-tubulin complexes.

Microtubules are major constituents of the cytoskeleton in all eukaryotic cells. They are essential for chromosome segregation during cell division, for directional intracellular transport and for building specialized cellular structures such as cilia or flagella. Their assembly has to be controlled spatially and temporally.

Nuclear alignment in myotubes requires centrosome proteins recruited by nesprin-1.

Myotubes are syncytial cells generated by fusion of myoblasts. Among the numerous nuclei in myotubes of skeletal muscle fibres, the majority are equidistantly positioned at the periphery, except for clusters of multiple nuclei underneath the motor endplate. The correct positioning of nuclei is thought to be important for muscle function and requires nesprin-1 (also known as SYNE1), a protein of the nuclear envelope.

Loss of Msp1p in Schizosaccharomyces pombe induces a ROS-dependent nuclear mutator phenotype that affects mitochondrial fission genes.

Mitochondria continually fuse and divide to dynamically adapt to changes in metabolism and stress. Mitochondrial dynamics are also required for mitochondrial DNA (mtDNA) integrity; however, the underlying reason is not known. In this study, we examined the link between mitochondrial fusion and mtDNA maintenance in Schizosaccharomyces pombe, which cannot survive without mtDNA, by screening for suppressors of the lethality induced by loss of the dynamin-related large GTPase Msp1p.

Processing of the dynamin Msp1p in S. pombe reveals an evolutionary switch between its orthologs Mgm1p in S. cerevisiae and OPA1 in mammals.

Mitochondrial fusion depends on the evolutionary conserved dynamin, OPA1/Mgm1p/Msp1p, whose activity is controlled by proteolytic processing. Since processing diverges between Mgm1p (Saccharomyces cerevisiae) and OPA1 (mammals), we explored this process in another model, Msp1p in Schizosaccharomyces pombe. Generation of the short isoform of Msp1p neither results from the maturation of the long isoform nor correlates with mitochondrial ATP levels.

The BH3-only Bnip3 binds to the dynamin Opa1 to promote mitochondrial fragmentation and apoptosis by distinct mechanisms.

Opa1 modulates mitochondrial fusion, cristae structure and apoptosis. The relationships between these functions and autosomal dominant optic atrophy, caused by mutations in Opa1, are poorly defined. We show that Bnip3 interacts with Opa1, leading to mitochondrial fragmentation and apoptosis.

Transmembrane segments of the dynamin Msp1p uncouple its functions in the control of mitochondrial morphology and genome maintenance.

Mitochondrial morphology depends on the equilibrium between antagonistic fission and fusion forces acting on mitochondrial membranes. Inactivation of fusion induces the loss of mtDNA. When both fusion and fission are simultaneously inactivated, the loss of mtDNA is alleviated, along with mitochondrial fragmentation.

Effects of OPA1 mutations on mitochondrial morphology and apoptosis: relevance to ADOA pathogenesis.

To characterize the molecular links between type-1 autosomal dominant optic atrophy (ADOA) and OPA1 dysfunctions, the effects of pathogenic alleles of this dynamin on mitochondrial morphology and apoptosis were analyzed, either in fibroblasts from affected individuals, or in HeLa cells transfected with similar mutants. The alleles were missense substitutions in the GTPase domain (OPA1(G300E) and OPA1(R290Q)) or deletion of the GTPase effector domain (OPA1(Delta58)). Fragmentation of mitochondria and apoptosis increased in OPA1(R290Q) fibroblasts and in OPA1(G300E) transfected HeLa cells.

The human macrophage mannose receptor is not a professional phagocytic receptor.

The macrophage mannose receptor (MR) appears to play an important role in the binding and phagocytosis of several human pathogens, but its phagocytic property and signaling pathways have been poorly defined. The general strategy to explore such topics is to express the protein of interest in nonphagocytic cells, but in the case of MR, there are few reports using the full-length MR cDNA. When we searched to clone de novo the human MR (hMR) cDNA, problems were encountered, and full-length hMR cDNA was only obtained after devising a complex cloning strategy.

Msp1p is an intermembrane space dynamin-related protein that mediates mitochondrial fusion in a Dnm1p-dependent manner in S. pombe.

Mitochondrial morphology is controlled by large GTPases, such as Msp1p, whose action on mitochondrial membranes is not yet understood. The sub-mitochondrial localization of Msp1p, the subject of ongoing controversies, was found to be within the intermembrane space. Overexpression of Msp1p led to aggregation of the mitochondrial network, while its downregulation resulted in fragmentation of this network.

The human dynamin-related protein OPA1 is anchored to the mitochondrial inner membrane facing the inter-membrane space.

Mutations in the OPA1 gene are associated with autosomal dominant optic atrophy. OPA1 encodes a dynamin-related protein orthologous to Msp1 of Schizosaccharomyces pombe and Mgm1p of Saccharomyces cerevisiae, both involved in mitochondrial morphology and genome maintenance. We present immuno-fluorescence and biochemical evidences showing that OPA1 resides in the mitochondria where it is imported through its highly basic amino-terminal extension.

MabA (FabG1), a Mycobacterium tuberculosis protein involved in the long-chain fatty acid elongation system FAS-II.

The fatty acid elongation system FAS-II is involved in the biosynthesis of mycolic acids, which are very long-chain fatty acids of the cell envelope specific to Mycobacterium tuberculosis and other mycobacteria. A potential component of FAS-II, the protein MabA (FabG1), was overexpressed and purified. Sedimentation equilibrium analyses revealed that MabA undergoes a dimer to tetramer self-association with a dissociation constant of 22 microM.

p59Hck isoform induces F-actin reorganization to form protrusions of the plasma membrane in a Cdc42- and Rac-dependent manner.

Hck is a protein kinase of the Src family specifically expressed in phagocytes as two isoforms, p59Hck and p61Hck, localized at the plasma membrane and lysosomes, respectively. Their individual involvement in functions ascribed to Hck, phagocytosis, cell migration, and lysosome mobilization, is still unclarified. To investigate the specific role of p59Hck, a constitutively active variant in fusion with green fluorescent protein (p59Hck(ca)) was expressed in HeLa cells.