Functional analysis of a recently originating, atypical presequence: mitochondrial import and processing of GUS fusion proteins in transgenic tobacco and yeast

Identification of three proteins involved in fertilization and parthenogenetic development of a brown alga, Scytosiphon lomentaria

Metabolic pathways of cell organelles may influence the expression of nuclear genes involved in fertilization and subsequent zygote development through a retrograde regulation. In Scytosiphon lomentaria, inheritance of chloroplast is biparental but mitochondria are maternally inherited. Male and female gametes underwent different parthenogenetic outcomes. Most (>99%) male gametes did not differentiate rhizoid cells or survived beyond four-cell stage, while over 95% of female gametes grew into mature asexual plants. Proteomic analysis showed that the protein contents of male and female gametes differed by approximately 1.7%, 12 sex-specific proteins out of 700 detected proteins. Three sex-specific proteins were isolated and identified using CAF-MALDI mass spectrometry and RACE-PCR. Among them, a male gamete-specific homoaconitate hydratase (HACN) and a female gamete-specific succinate semialdehyde dehydrogenase (SSADH) were predicted to be the genes involved in mitochondrial metabolic pathways. The expression level of both mitochondrial genes was dramatically changed at the fertilization event. During parthenogenetic development the male-specific HACN and GTP-binding protein were gradually down-regulated but SSADH stayed up-regulated up to 48h. To observe the effect of chemicals on the expression of these genes, male and female gametes were treated with γ-aminobutyric acid (GABA), hydrogen peroxide and L-ascorbic acid. Among them GABA treatment significantly reduced SSADH gene expression in female gamete but the same treatment induced high upregulation of the gene in male gamete. GABA treatment affected the behavior of gametes and their parthenogenetic development. Both gametes showed prolonged motile stage, retarded settlement and subsequent parthenogenetic development. Our results suggest that male and female gametes regulate mitochondrial metabolic pathways differentially during fertilization, which may be the reason for their physiological and behavioral differences.

A member of a novel Arabidopsis thaliana gene family of candidate Mg2+ ion transporters complements a yeast mitochondrial group II intron-splicing mutant

Autocatalytic activity of some group II introns has been demonstrated in vitro, but helper functions such as the yeast MRS2 protein are essential for splicing in vivo. In our search for such helper factors in plants, we pursued the cloning of two Arabidopsis thaliana homologues, atmrs2-1 and atmrs2-2. Atmrs2-1, but not atmrs2-2, complements the yeast deletion mutant of mrs2, and this is congruent with the prediction of two adjacent transmembrane stretches in AtMRS2-1 and yeast MRS2 but not in AtMRS2-2. This complementation depends on fusion of the native yeast mitochondrial import sequence to atmrs2-1. A differing, non-mitochondrial, cellular targeting in Arabidopsis is supported by the analysis of green fluorescent protein fusion constructs after transient transformation into plant protoplasts. Further members of what now appears to be a family of 10 mrs2 homologues are identified in the Arabidopsis genome. Similarity searches with the PSI-BLAST algorithm in the protein database fail to identify homologues of this novel gene family in any eukaryotes other than yeasts, but do identify its distant relatedness to the corA group of bacterial magnesium transporters. In line with this observation, intramitochondrial magnesium concentrations are indeed restored to wild-type levels in the yeast mutant on complementation with atmrs2-1.

Catalytic DNA- and RNA-hydrolyzing antibodies from milk of healthy human mothers

Various catalytically active antibodies (Abs), or abzymes, have been detected recently in the sera of patients with autoimmune pathologies, in whom their presence is probably associated with autoimmunization. Normal humans are generally not considered to have abzymes, since no obvious immunizing factors are present. Here is shown by different methods that IgG from the milk of normal females possesses both DNase and RNase activities. The activities were also present in the IgG F(ab')2 and Fab fragments. Affinity modification of IgG by the chemically reactive derivative of an oligonucleotide led to preferential modification of the L chain of IgG. After separation of the subunits by sodium dodecyl sulfate electrophoresis in a gel containing DNA, an in-gel assay showed DNase activity in the L chain. The L chain separated by affinity chromatography on DNA-cellulose was catalytically active. These findings speak in favor of the generation of catalytic Abs by the immune system of healthy mothers. It is known that the treatment of adults with DNases and RNases offers protection from viral and bacterial diseases. Since breast milk protects the infants from infections until the immune system is developed, this raises the possibility that catalytic Abs like nucleases, may possess a protective role.

Secretory immunoglobulin A from human milk catalyzes milk protein phosphorylation

This article presents evidence that protein kinase activity is an intrinsic property of secretory immunoglobulin A (sIgA) from milk of healthy human mothers. Polyclonal sIgA was purified by sequential chromatography on protein A-Sepharose, DEAE-cellulose, and gel filtration on Toyopearl HW-55 and Sepharose 4B columns. Its purity was established by one- and two-dimensional SDS-PAGE. The protein kinase activity was inhibited by specific antibodies (Abs) against sIgA, and was stable to acidic and alkaline conditions. Catalytic sIgA showed optimal reaction conditions (pH and MgCl2 concentration) and substrate specificity different from those of known protein kinases; i.e., sIgA phosphorylated the serine residues of various milk proteins in the presence of different gamma-[32P]nucleoside- and deoxynucleoside-5'-triphosphates. The homogeneous Fab fragment of sIgA also showed kinase activity. An ATP-binding activity of fractions of sIgA was demonstrated by affinity chromatography on ATP-Sepharose and by covalent binding of an affinity analog of ATP; this activity was mediated by the L chain of sIgA. The authors believe these observations are the first example of the catalytic activity of IgA Abs and of natural catalytic Abs with synthetic activity. In addition, the findings suggest the likelihood that catalytic Abs are generated by the immune system of healthy mothers.

DNA-hydrolyzing activity of the light chain of IgG antibodies from milk of healthy human mothers

Various catalytically active antibodies or abzymes have been detected recently in the sera of patients with several autoimmune pathologies, where their presence is most probably associated with autoimmunization. Normal humans are generally considered to have no abzymes, since no obvious immunizing factors are present. Recently we have shown that IgG (its Fab and F(ab)2 fragments) from the milk of normal humans possesses DNase activity. Here we demonstrate for the first time that the light chain of IgG catalyzes the reaction of DNA hydrolysis. These findings speak in favor of the generation of abzymes in the tissue of healthy mothers, and since a mother's breast milk protects her infant from infections until the immune system is developed, they raise the possibility that these abzymes may contribute to this protective role.