Essential role of Mia40 in import and assembly of mitochondrial intermembrane space proteins

Mitochondria import nuclear-encoded precursor proteins to four different subcompartments. Specific import machineries have been identified that direct the precursor proteins to the mitochondrial outer membrane, inner membrane or matrix, respectively. However, a machinery dedicated to the import of mitochondrial intermembrane space (IMS) proteins has not been found so far. We have identified the essential IMS protein Mia40 (encoded by the Saccharomyces cerevisiae open reading frame YKL195w). Mitochondria with a mutant form of Mia40 are selectively inhibited in the import of several small IMS proteins, including the essential proteins Tim9 and Tim10. The import of proteins to the other mitochondrial subcompartments does not depend on functional Mia40. The binding of small Tim proteins to Mia40 is crucial for their transport across the outer membrane and represents an initial step in their assembly into IMS complexes. We conclude that Mia40 is a central component of the protein import and assembly machinery of the mitochondrial IMS.     

Plasmalemmal vacuolar-type H+-ATPase in cancer biology

Vacuolar-type H⁺-adenosine triphosphatase (V-ATPase) is one of the most fundamental enzymes in nature. V-ATPases are responsible for the regulation of proton concentration in the intracellular acidic compartments. It has similar structure with the mitochondrial F₀F₁-ATP synthase (F-ATPase).^† The V-ATPases are composed of multiple subunits and have various physiological functions, including membrane and organelle protein sorting, neurotransmitter uptake, cellular degradative processes, and cytosolic pH regulation. The V-ATPases have been involved in multidrug resistance. Recently, plasma membrane V-ATPases have been involved in regulation of extracellular acidity, essential for cellular invasiveness and proliferation in tumor metastasis. The current knowledge regarding the structure and function of V-ATPase and its role in cancer biology is discussed. F in F₀F₁ ATPase is the coupling energy factor.     

Characteristics of arylsulfatase in Russian sturgeon (Acipenser gueldenstaedti) semen

Spermatozoa of sturgeons (Acipenseriformes), unlike teleosts, possess an acrosome. This paper provides data concerning biochemical characteristics of arylsulfatase (AS), an acrosomal enzyme, found in Russian sturgeon spermatozoa and seminal plasma. The enzymes were purified by a four-step procedure, using n-butanol extraction, ion-exchange chromatography repeated twice and gel filtration. High purity of our enzymes was confirmed by silver staining electrophoresis and an immunological experiment. Kinetic parameters indicated that the purified enzymes belong to arylsulfatase type A. Similarity of the seminal plasma arylsulfatase to the spermatozoan enzyme showed us that arylsulfatase from seminal plasma might originate from damaged spermatozoa. The possible physiological consequences of the presence of arylsulfatase in Russian sturgeon semen are discussed.     

Prediction of the coding sequences of mouse homologues of FLJ genes: the complete nucleotide sequences of 110 mouse FLJ-homologous cDnas identified by screening of terminal sequences of cDNA clones randomly sampled from size-fractionated libraries.

We have been conducting a mouse cDNA project to predict protein-coding sequences of mouse KIAA-homologous genes since 2001. As an extension of this project, we also started to accumulate mouse cDNA clones homologous to the human FLJ cDNA clones which are another long cDNA resource produced in our institute. We have isolated the cDNA clones from size-fractionated cDNA libraries derived from five different mouse tissues and natural killer T-cells. Although the human FLJ cDNA clones were originally derived from human spleen libraries, one-third of their mouse homologues were obtained from the brain library. We designated these homologues "mFLJ" plus a 5-digit number and herein characterized 110 mFLJ cDNA clones. We assigned an integrity of the CDSs from the comparison of the 110 cDNA clones with the corresponding human FLJ cDNA clones. The average size of the 110 mouse cDNA sequences was 3.8 kb and that of the deduced amino acid sequences from their longest CDS in each cDNA was 663 amino acid residues. Homology and/or motif search against public databases revealed new domains and/or motifs in 26 mFLJ gene products which provide additional speculation regarding the function of FLJ genes.     

Small GTPases in vesicle trafficking

Plant small GTPases belonging to the Rop, Arf, and Rab families are regulators of vesicle trafficking. Rop GTPases regulate actin dynamics and modulate H(2)O(2) production in polar cell growth and pathogen defence. A candidate Rop GDP to Rop GTP exchange factor (RopGEF) SPIKE1 is involved in the morphogenesis of leaf epidermal cells. The ArfGEF GNOM regulates the endosomal recycling of the PIN proteins, which are involved in polar auxin transport. Intracellular localisation of small GTPases and functional studies using dominant mutant versions of Arf and Rab GTPases are defining novel plant-specific membrane compartments, especially those that participate in endosomal vesicle trafficking.     

Membrane trafficking in plants: new discoveries and approaches

The general organization and function of the endomembrane system is highly conserved in eukaryotic cells. In addition, increasing numbers of studies demonstrate that normal plant growth and development are dependent on specialized tissue and subcellular-specific components of the plant membrane trafficking machinery. New approaches, including chemical genomics and proteomics, will likely accelerate our understanding of the diverse functions of the plant endomembrane system.     

Lipid function in plant cell polarity

The establishment and maintenance of cell polarity play pivotal roles during plant development. During the past five years, proteins that are required for different aspects of plant cell polarity have been identified. However, the functions of lipids and their interactions with proteins that mediate polarity remained largely unaddressed. Recent genetic studies have discovered cell and tissue polarity mutants that have defects in sterol composition, glycosylphosphatidylinositol-anchored proteins, glycosylphosphatidylinositol biosynthesis and phospholipid signalling. Analyses of the affected gene products have provided a first glance at the roles of lipids in cell polarity signalling, as well as in the trafficking and anchoring of polar proteins.