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The topological specificity factor AtMinE1 is essential for correct plastid division site placement in Arabidopsis.

In plant cells, plastids divide by binary fission involving a complex pathway of events. Although there are clear similarities between bacterial and plastid division, limited information exists regarding the mechanism of plastid division in higher plants. Here we demonstrate that AtMinE1, an Arabidopsis homologue of the bacterial MinE topological specificity factor, is an essential integral component of the plastid division machinery. In prokaryotes MinE imparts topological specificity during cell division by blocking division apparatus assembly at sites other than midcell. We demonstrate that overexpression of AtMinE1 in E. coli results in loss of topological specificity and minicell formation suggesting evolutionary conservation of MinE mode of action. We further show that AtMinE1 can indeed act as a topological specificity factor during plastid division revealing that AtMinE1 overexpression in Arabidopsis seedlings results in division site misplacement giving rise to multiple constrictions along the length of plastids. In agreement with cell division studies in bacteria, AtMinE1 and AtMinD1 show distinct intraplastidic localisation patterns suggestive of dynamic localisation behaviour. Taken together our findings demonstrate that AtMinE1 is an evolutionary conserved topological specificity factor, most probably acting in concert with AtMinD1, required for correct plastid division in Arabidopsis.

Arabidopsis↗

Extent and limitation of the control of nuclear apoptosis by DNA-fragmenting factor.

During apoptosis, changes to the nucleus of the dying cell include DNA degradation and structural collapse. These changes are accomplished by caspase-mediated cleavage of DNA-fragmenting factor DFF45, an inhibitor of the effector molecule DFF40. DFF45 and, more efficiently, a mutant lacking one caspase-cleavage site (DFF45m) inhibited nuclear changes in a cell-free system when apoptosis was initiated by adding caspase-3 to cell extracts. In primary tissues from several mammalian species, human caspase-3 activated and human DFF45m blocked nuclear apoptosis demonstrating evolutionary conservation of this step. However, DFF45m did not significantly inhibit DNA-fragmenting activity in extracts from staurosporine-treated cells from the human cell line Jurkat. In extracts from normal Jurkat cells, DFF45m blocked caspase-triggered DNA cleavage efficiently only if added within a short time of the addition of the caspase. At later time points, this inhibition by DFF45m was strongly reduced in efficiency while Zn2+ still completely blocked DNA fragmentation. These results demonstrate the evolutionary conservation of a linear pathway in apoptosis and suggest the existence of more complex events as final effector machinery.

Animals↗

[Evolution of RNA-dependent RNA-polymerases from positive RNA viruses: comparison of phylogenetic trees constructed by different methods].

Presumptive phylogenetic trees of evolutionary conserved fragments of RNA-dependent RNA polymerases of 26 positive strand RNA viruses were generated using a simple clustering procedure or a novel approach based on the so-called maximal topologic similarity principle. The latter methodology involves a quantitative measure of the degree of correspondence between the topology of generated trees and structure of the initial distance matrix. The algorithm for tree construction based on the maximal topologic similarity principle does not include the assumption of evolutionary rate constancy, as opposed to the clustering procedure. Nevertheless, it is demonstrated that the trees generated by the two methods are topologically similar, indicating that no drastic change of evolutionary rate had occurred in evolution of the positive strand RNA virus RNA polymerases. This in turn suggests that RNA-dependent RNA polymerases (or at least their evolutionary conserved core domains used for construction of the phylogenetic trees) are principally functionally equivalent in all positive strand RNA viruses.

Algorithms↗

AtNAP1 represents an atypical SufB protein in Arabidopsis plastids.

The assembly of iron-sulfur (Fe-S) clusters involves several pathways and in prokaryotes the mobilization of the sulfur (SUF) system is paramount for Fe-S biogenesis and repair during oxidative stress. The prokaryotic SUF system consists of six proteins: SufC is an ABC/ATPase that forms a complex with SufB and SufD, SufA acts as a scaffold protein, and SufE and SufS are involved in sulfur mobilization from cysteine. Despite the importance of Fe-S proteins in higher plant plastids, little is known regarding plastidic Fe-S cluster assembly. We have recently shown that Arabidopsis harbors an evolutionary conserved plastidic SufC protein (AtNAP7) capable of hydrolyzing ATP and interacting with the SufD homolog AtNAP6. Based on this and the prokaryotic SUF system we speculated that a SufB-like protein may exist in plastids. Here we demonstrate that the Arabidopsis plastid-localized SufB homolog AtNAP1 can complement SufB deficiency in Escherichia coli during oxidative stress. Furthermore, we demonstrate that AtNAP1 can interact with AtNAP7 inside living chloroplasts suggesting the presence of a plastidic AtNAP1.AtNAP6.AtNAP7 complex and remarkable evolutionary conservation of the SUF system. However, in contrast to prokaryotic SufB proteins with no associated ATPase activity we show that AtNAP1 is an iron-stimulated ATPase and that AtNAP1 is capable of forming homodimers. Our results suggest that AtNAP1 represents an atypical plastidic SufB-like protein important for Fe-S cluster assembly and for regulating iron homeostasis in Arabidopsis.

Adenosine Triphosphatases↗

Cloning, characterization, and embryonic expression analysis of the Drosophila melanogaster gene encoding insulin/relaxin-like peptide.

Insulin is one of the key peptide hormones that regulates growth and metabolism in vertebrates. Evolutionary conservation of many elements of the insulin/IGF signaling network makes it possible to study the basic genetic function of this pathway in lower metazoan models such as Drosophila. Here we report the cloning and characterization of the gene for Drosophila insulin/relaxin-like peptide (DIRLP). The predicted protein structure of DIRLP greatly resembles typical insulin structure and contains features that differentiate it from the Drosophila juvenile hormone, another member of the insulin family. The Dirlp gene is represented as a single copy in the Drosophila melanogaster genome (compared to multiple copies for Drosophila juvenile hormone) and shows evolutionary conservation of genetic structure. The gene was mapped to the Drosophila chromosome 3, region 67D2. In situ hybridization of whole-mount Drosophila embryos with Dirlp antisense RNA probe reveals early embryonic mesodermal/ventral furrow expression pattern, consistent with earlier observation of the insulin protein immunoreactivity in Drosophila embryos. The in situ hybridization pattern was found to be identical to that obtained during immunohistochemistry analysis of the Drosophila embryos using various insulin monoclonal and polyclonal antibodies that do not recognize Drosophila juvenile hormone, supporting the idea that Dirlp is a possible Drosophila insulin ortholog. Identification of the gene for DIRLP provides a new approach for study of the regulatory pathway of the insulin family of peptides.

Amino Acid Sequence↗

The follicle-stimulating hormone beta-subunit gene of the common brushtail possum (Trichosurus vulpecula): analysis of cDNA sequence and expression.

Reverse transcription-PCR has been used to obtain a cDNA sequence from the follicle-stimulating hormone (FSH) beta-subunit gene of the Australian brushtail possum (Trichosurus vulpecula). Comparisons of the possum FSHbeta-mRNA coding region nucleotide sequence with that of six eutherian mammal homologues reveals a mean percent identity of 77.3% and 76.8% at the nucleotide and predicted amino acid-sequence levels respectively. Furthermore, the predicted amino acid sequence of the possum FSHbeta mature protein shows evolutionary conservation of twelve cysteine residues and two potential N-linked glycosylation sites. The protein lacks the CAGY motif present in most reported glycoprotein beta-subunit sequences. The translation termination codon and consensus polyadenylation sequence overlap, a feature observed in other mammalian FSHbeta genes. Northern hybridization of total RNA from adult female possum pituitary revealed three hybridizing transcripts of approximately 2.8, 1.2 and 0.5 kb which may arise from utilizing alternative polyadenylation signals. In situ hybridization localized the FSHbeta transcripts to a sub-population of anterior pituitary cells interpreted as being gonadotropes. In summary the results indicate considerable evolutionary conservation of the structure of the FSH beta-subunit gene between the marsupial and eutherian mammalian lineages.

Adult↗

Improvement in protein functional site prediction by distinguishing structural and functional constraints on protein family evolution using computational design.

The prediction of functional sites in newly solved protein structures is a challenge for computational structural biology. Most methods for approaching this problem use evolutionary conservation as the primary indicator of the location of functional sites. However, sequence conservation reflects not only evolutionary selection at functional sites to maintain protein function, but also selection throughout the protein to maintain the stability of the folded state. To disentangle sequence conservation due to protein functional constraints from sequence conservation due to protein structural constraints, we use all atom computational protein design methodology to predict sequence profiles expected under solely structural constraints, and to compute the free energy difference between the naturally occurring amino acid and the lowest free energy amino acid at each position. We show that functional sites are more likely than non-functional sites to have computed sequence profiles which differ significantly from the naturally occurring sequence profiles and to have residues with sub-optimal free energies, and that incorporation of these two measures improves sequence based prediction of protein functional sites. The combined sequence and structure based functional site prediction method has been implemented in a publicly available web server.

Algorithms↗

Accurate prediction of the functional significance of single nucleotide polymorphisms and mutations in the ABCA1 gene.

The human genome contains an estimated 100,000 to 300,000 DNA variants that alter an amino acid in an encoded protein. However, our ability to predict which of these variants are functionally significant is limited. We used a bioinformatics approach to define the functional significance of genetic variation in the ABCA1 gene, a cholesterol transporter crucial for the metabolism of high density lipoprotein cholesterol. To predict the functional consequence of each coding single nucleotide polymorphism and mutation in this gene, we calculated a substitution position-specific evolutionary conservation score for each variant, which considers site-specific variation among evolutionarily related proteins. To test the bioinformatics predictions experimentally, we evaluated the biochemical consequence of these sequence variants by examining the ability of cell lines stably transfected with the ABCA1 alleles to elicit cholesterol efflux. Our bioinformatics approach correctly predicted the functional impact of greater than 94% of the naturally occurring variants we assessed. The bioinformatics predictions were significantly correlated with the degree of functional impairment of ABCA1 mutations (r2 = 0.62, p = 0.0008). These results have allowed us to define the impact of genetic variation on ABCA1 function and to suggest that the in silico evolutionary approach we used may be a useful tool in general for predicting the effects of DNA variation on gene function. In addition, our data suggest that considering patterns of positive selection, along with patterns of negative selection such as evolutionary conservation, may improve our ability to predict the functional effects of amino acid variation.

ATP Binding Cassette Transporter 1↗

Open reading frames provide a rich pool of potential natural antisense transcripts in fungal genomes.

Natural antisense transcripts are reported from all kingdoms of life and several recent reports of genomewide screens indicate that they are widely distributed. These transcripts seem to be involved in various biological functions and may govern the expression of their respective sense partner. Very little, however, is known about the degree of evolutionary conservation of antisense transcripts. Furthermore, none of the earlier analyses has studied whether antisense relationships are solely dual or involved in more complex relationships. Here we present a systematic screen for cis- and trans-located antisense transcripts based on open reading frames (ORFs) from five fungal species. The relative number of ORFs involved in antisense relationships varies greatly between the five species. In addition, other significant differences are found between the species, such as the mean length of the antisense region. The majority of trans-located antisense transcripts is found to be involved in complex relationships, resulting in highly connected networks. The analysis of the degree of evolutionary conservation of antisense transcripts shows that most antisense transcripts have no ortholog in any other species. An annotation of antisense transcripts based on Gene Ontology directs to common terms and shows that proteins of genes involved in antisense relationships preferentially localize to the nucleus with common functions in the regulation or maintenance of nucleic acids.

Evolution, Molecular↗

Spatial distribution of Reissner's fiber glycoproteins in the filum terminale of the rat and rabbit.

The subcommissural organ secretes into the third ventricle glycoproteins that condense to form the Reissner's fiber (RF). At the distal end of the central canal of the spinal cord, the RF-glycoproteins accumulate in the form of an irregular mass known as massa caudalis. Antibodies against RF-glycoproteins and a set of lectins were used at the light and electron microscopic level to investigate the spatial distribution of the massa caudalis material in the rat and rabbit filum terminale. In the sacral region of the rat, the central canal presents gaps between the ependymal cells through which RF-glycoproteins spread out. The bulk of massa caudalis material, however, escapes through openings in the dorsal wall of the terminal ventricle. In the rabbit, the massa caudalis is formed within the ependymal canal, at the level of the second coccygeal vertebra, it accumulates within preterminal and terminal dilatations of the central canal, and it escapes out through gaps in the dorsal ependymal wall of the terminal ventricle. The existence of wide intercellular spaces and a large orifice (neuroporous) in the dorsal ependymal wall of the terminal ventricle, and the passage of RF-material through them, appear to be conserved evolutionary features. After leaving the terminal ventricle of the rat and rabbit, RF-glycoproteins establish a close spatial association with the numerous blood vessels irrigating the filum terminale, suggesting that in these species the blood vessels are the site of destination of the RF-glycoproteins escaping from the central canal, thus resembling the situation found in lower vertebrates. When passing from the RF stage to the massa caudalis stage, the rabbit RF-glycoproteins lose their sialic acid residues, exposing galactose as the terminal residue. Since this sialic acid-galactose modification of RF-glycoproteins had also been described in lamprey larvae, it may be regarded as a conserved evolutionary feature associated with the formation of the massa caudalis.

Animals↗

The telomeric region of BTA18 containing a potential QTL region for health in cattle exhibits high similarity to the HSA19q region in humans.

We have applied a targeted physical mapping approach, based on the isolation of bovine region-specific large-insert clones using homologous human sequences and chromosome microdissection, to enhance the physical gene map of the telomeric region of BTA18 and to prove its evolutionary conservation. The latter is a prerequisite to exploit the dense human gene map for future positional cloning approaches. Partial sequencing and homology search were used to characterize 20 BACs targeted to the BTA18q2.4-q2.6 region. We used fluorescence in situ hybridization (FISH) to create physical maps of 11 BACs containing 15 gene loci; these BACs served as anchor loci. Using these approaches, 12 new gene loci (CKM, STK13, PSCD2, IRF3, VASP, ACTN4, ITPKC, CYP2B6, FOSB, DMPK, MIA, SIX5) were assigned on BTA18 in the bovine cytogenetic map. A resolved physical map of BTA18q2.4-q2.6 was developed, which encompasses 28 marker loci and a comparative cytogenetic map that contains 15 genes. The mapping results demonstrate the high evolutionary conservation between the telomeric region of BTA18q and HSA19q.

Animals↗

Genomic organization and functional analysis of the gene encoding the Krüppel-like transcription factor KLF6.

The Krüppel-like transcription Factor 6 (KLF6) is regulated during cell proliferation and differentiation events like mammalian development and tissue regeneration, while its aberrant expression is associated with tumor formation. To investigate KLF6 transcriptional control, the genomic organization of human KLF6 together with its cis-regulatory region was analyzed. A high sequence homology of KLF6 regulatory regions was found in mammals, which in turn predicts a high degree of evolutionary conserved transcriptional mechanisms. A transcription start site was identified at the first nucleotide downstream of a potential initiator element. Also, the role of KLF6 regulatory regions was determined by transfection experiments. A minimal promoter region lacking a TATA-box yet containing an Initiator was identified and found to be active in all cells analyzed. In addition, two strong activating sequences were located between positions -407/-344 and -307/-207, where the latter contained Sp1 and CAAT-box sites. Furthermore, ectopic expression of Sp1 increased the transcriptional activity of the KLF6 promoter. In conclusion, our data revealed that KLF6 gene transcription is under control of a TATA-box independent initiation mechanism together with an evolutionary conserved array of positive cis-acting elements.

Animals↗

Molecular characterization and evidencing of the porcine CRH gene as a functional-positional candidate for growth and body composition.

Corticotropin-releasing hormone (CRH), a major regulator of neuroendocrine response to stress, is involved in the control of energy balance and thus may affect body composition and growth. The porcine CRH (pCRH) gene was studied as a comparative-positional candidate for QTL for longissimus muscle area, average backfat thickness, carcass length, and average daily gain on test on porcine chromosome 4. Sequence of the complete transcriptional unit of pCRH gene spanning 2068bp was determined along with 582bp of the 5'-flanking region. Cross-species sequence comparison revealed a number of potential regulatory regions including an intronic evolutionary conserved region and an adjacent CpG island that may control cell-type specific expression of the CRH gene. A SNP in exon 2 (c.+83G>A) leading to a non-conservative amino acid exchange (p.28Arg>Gln) in the prohormone was identified that is segregating in the DUMI resource population. Linkage and association analysis based on this SNP revealed that for all four traits the pCRH gene falls in the QTL peak area and that the c.+83G>A SNP shows a highly significant additive effect (p<0.0001). Physical mapping using the IMpRH panel assigned the pCRH gene to interval SW724-S0107, promoting the gene as a positional candidate also for QTL identified in other porcine resource populations. Additional four variable sites were identified that segregate in commercial pig breeds. Particularly interesting is a SNP (g.233C>T) in the 5'-flanking region that occurred in an evolutionary conserved motif. The knowledge of the DNA-variation of pCRH gene will facilitate follow-up studies necessary to provide definite genetic evidence of the effect of pCRH gene on body composition and growth.

Amino Acid Sequence↗

Immunostimulatory properties of the Leishmania infantum heat shock proteins HSP70 and HSP83.

Emerging evidence indicates that the heat shock proteins (HSPs), a set of highly evolutionary conserved proteins, are playing essential roles in both normal processes of the immune system and specific immune responses. In a previous work, we demonstrated that the Leishmania infantum HSP70 possesses remarkable immunostimulatory properties. In the present work, we have extended the study to another HSP from this parasite, the HSP83. We show that this protein also has an adjuvant effect to an accompanying protein by stimulation of the humoral response when both proteins are fused and co-administered to BALBjc mice. The analysis of the IgG isotypes, IgG1 and IgG2a, indicated that the immunisations with the Leishmania HSPs, mainly the HSP70, potentiate a Thl-type response. It was found that the amino-terminal domain of the HSP70, the most evolutionary conserved region of the molecule, maintains the ability to stimulate the humoral response, whereas the carboxyl-terminal domain does not have a similar effect. Unexpectedly, we found that the L. infantum HSP70 and HSP83 recombinant proteins stimulated the proliferation of spleen cells from unprimed BALB/c mice. Remarkably, this proliferation was abolished either by thermal denaturing of the proteins or by using specific antibodies. The use of the T-cell inhibitor cyclosporin A in the splenocytes proliferation assays suggested that both T- and non-T-cells are stimulated by the Leishmania HSPs. These findings may be relevant for therapeutic and prophylactic applications.

Adjuvants, Immunologic↗

WIPI-1alpha (WIPI49), a member of the novel 7-bladed WIPI protein family, is aberrantly expressed in human cancer and is linked to starvation-induced autophagy.

WD-repeat proteins are regulatory beta-propeller platforms that enable the assembly of multiprotein complexes. Here, we report the functional and bioinformatic analysis of human WD-repeat protein Interacting with PhosphoInosides (WIPI)-1alpha (WIPI49/Atg18), a member of a novel WD-repeat protein family with autophagic capacity in Saccharomyces cerevisiae and Caenorhabditis elegans, recently identified as phospholipid-binding effectors. Our phylogenetic analysis divides the WIPI protein family into two paralogous groups that fold into 7-bladed beta-propellers. Structural modeling identified two evolutionary conserved interaction sites in WIPI propellers, one of which may bind phospholipids. Human WIPI-1alpha has LXXLL signature motifs for nuclear receptor interactions and binds androgen and estrogen receptors in vitro. Strikingly, human WIPI genes were found aberrantly expressed in a variety of matched tumor tissues including kidney, pancreatic and skin cancer. We found that endogenous hWIPI-1 protein colocalizes in part with the autophagosomal marker LC3 at punctate cytoplasmic structures in human melanoma cells. In addition, hWIPI-1 accumulated in large vesicular and cup-shaped structures in the cytoplasm when autophagy was induced by amino-acid deprivation. These cytoplasmic formations were blocked by wortmannin, a classic inhibitor of PI-3 kinase-mediated autophagy. Our data suggest that WIPI proteins share an evolutionary conserved function in autophagy and that autophagic capacity may be compromised in human cancers.

Amino Acid Sequence↗

Ionizing radiation-induced foci formation of mammalian Rad51 and Rad54 depends on the Rad51 paralogs, but not on Rad52.

Homologous recombination is of major importance for the prevention of genomic instability during chromosome duplication and repair of DNA damage, especially double-strand breaks. Biochemical experiments have revealed that during the process of homologous recombination the RAD52 group proteins, including Rad51, Rad52 and Rad54, are involved in an essential step: formation of a joint molecule between the broken DNA and the intact repair template. Accessory proteins for this reaction include the Rad51 paralogs and BRCA2. The significance of homologous recombination for the cell is underscored by the evolutionary conservation of the Rad51, Rad52 and Rad54 proteins from yeast to humans. Upon treatment of cells with ionizing radiation, the RAD52 group proteins accumulate at the sites of DNA damage into so-called foci. For the yeast Saccharomyces cerevisiae, foci formation of Rad51 and Rad54 is abrogated in the absence of Rad52, while Rad51 foci formation does occur in the absence of the Rad51 paralog Rad55. By contrast, we show here that in mammalian cells, Rad52 is not required for foci formation of Rad51 and Rad54. Furthermore, radiation-induced foci formation of Rad51 and Rad54 is impaired in all Rad51 paralog and BRCA2 mutant cell lines tested, while Rad52 foci formation is not influenced by a mutation in any of these recombination proteins. Despite their evolutionary conservation and biochemical similarities, S. cerevisiae and mammalian Rad52 appear to differentially contribute to the DNA-damage response.

Animals↗

A new method to model membrane protein structure based on silent amino acid substitutions.

The importance of accurately modeling membrane proteins cannot be overstated, in lieu of the difficulties in solving their structures experimentally. Often, however, modeling procedures (e.g., global searching molecular dynamics) generate several possible candidates rather then pointing to a single model. Herein we present a new approach to select among candidate models based on the general hypothesis that silent amino acid substitutions, present in variants identified from evolutionary conservation data or mutagenesis analysis, do not affect the stability of a native structure but may destabilize the non-native structures also found. The proof of this hypothesis has been tested on the alpha-helical transmembrane domains of two homodimers, human glycophorin A and human CD3-zeta, a component of the T-cell receptor. For both proteins, only one structure was identified using all the variants. For glycophorin A, this structure is virtually identical to the structure determined experimentally by NMR. We present a model for the transmembrane domain of CD3-zeta that is consistent with predictions based on mutagenesis, homology modeling, and the presence of a disulfide bond. Our experiments suggest that this method allows the prediction of transmembrane domain structure based only on widely available evolutionary conservation data.

Amino Acid Substitution↗

Role of protein kinase C-mediated protein phosphorylation in mitochondrial translocation of mouse CYP1A1, which contains a non-canonical targeting signal.

A large number of mitochondrial proteins lack canonical mitochondrial-targeting signals. The bimodal transport of cytochromes P450 (CYPs) to endoplasmic reticulum and mitochondria (MT), reported previously by us, likely represents one mode of non-canonical protein targeting to MT. Herein, we have studied the mechanism of mouse MT-CYP1A1 targeting to gain insight into the regulatory features and evolutionary conservation of bimodal targeting mechanism. Mouse MT-CYP1A1 consists of two NH2-terminal-truncated molecular species, +91A1 and +331A1. Mutations Pro-2 --> Leu and Tyr-5 --> Leu, which increase the signal recognition particle (SRP) binding, diminished MT targeting of the protein in intact cells. By contrast, mutations Leu-7 --> Asn and Leu-17 --> Asn, which decreased SRP-binding affinity, enhanced MT targeting, thus suggesting that SRP binding is an important regulatory step that modulates bimodal targeting. Protein kinase C (PKC)-mediated phosphorylation of nascent chains at Thr-35 vastly decreased affinity for SRP binding suggesting an important regulatory step. In support of these results, COS cell transfection experiments show that phosphomimetic mutation Thr-35 --> Asp or induced cellular PKC caused increased CYP1A1 targeting to MT and correspondingly lower levels to the endoplasmic reticulum. Results suggest evolutionary conservation of chimeric signals and bimodal targeting of CYP1A1 in different species. The mouse MT-CYP1A1 is an extrinsic membrane protein, which exhibited high FDX1 plus FDXR-mediated N-demethylation of a number of tricyclic antidepressants, pain killers, anti-psychotics, and narcotics that are poor substrates for microsomal CYP1A1.

Amino Acid Sequence↗