Non-homologous isofunctional enzymes: A systematic analysis of alternative solutions in enzyme evolution

<p>Abstract</p> <p>Background</p> <p>Evolutionarily unrelated proteins that catalyze the same biochemical reactions are often referred to as analogous - as opposed to homologous - enzymes. The existence of numerous alternative, non-homologous enzyme isoforms presents an interesting evolutionary problem; it also complicates genome-based reconstruction of the metabolic pathways in a variety of organisms. In 1998, a systematic search for analogous enzymes resulted in the identification of 105 Enzyme Commission (EC) numbers that included two or more proteins without detectable sequence similarity to each other, including 34 EC nodes where proteins were known (or predicted) to have distinct structural folds, indicating independent evolutionary origins. In the past 12 years, many putative non-homologous isofunctional enzymes were identified in newly sequenced genomes. In addition, efforts in structural genomics resulted in a vastly improved structural coverage of proteomes, providing for definitive assessment of (non)homologous relationships between proteins.</p> <p>Results</p> <p>We report the results of a comprehensive search for non-homologous isofunctional enzymes (NISE) that yielded 185 EC nodes with two or more experimentally characterized - or predicted - structurally unrelated proteins. Of these NISE sets, only 74 were from the original 1998 list. Structural assignments of the NISE show over-representation of proteins with the TIM barrel fold and the nucleotide-binding Rossmann fold. From the functional perspective, the set of NISE is enriched in hydrolases, particularly carbohydrate hydrolases, and in enzymes involved in defense against oxidative stress.</p> <p>Conclusions</p> <p>These results indicate that at least some of the non-homologous isofunctional enzymes were recruited relatively recently from enzyme families that are active against related substrates and are sufficiently flexible to accommodate changes in substrate specificity.</p> <p>Reviewers</p> <p>This article was reviewed by Andrei Osterman, Keith F. Tipton (nominated by Martijn Huynen) and Igor B. Zhulin. For the full reviews, go to the Reviewers' comments section.</p

Comparative genomics of Thermus thermophilus and Deinococcus radiodurans: divergent routes of adaptation to thermophily and radiation resistance

BACKGROUND: Thermus thermophilus and Deinococcus radiodurans belong to a distinct bacterial clade but have remarkably different phenotypes. T. thermophilus is a thermophile, which is relatively sensitive to ionizing radiation and desiccation, whereas D. radiodurans is a mesophile, which is highly radiation- and desiccation-resistant. Here we present an in-depth comparison of the genomes of these two related but differently adapted bacteria. RESULTS: By reconstructing the evolution of Thermus and Deinococcus after the divergence from their common ancestor, we demonstrate a high level of post-divergence gene flux in both lineages. Various aspects of the adaptation to high temperature in Thermus can be attributed to horizontal gene transfer from archaea and thermophilic bacteria; many of the horizontally transferred genes are located on the single megaplasmid of Thermus. In addition, the Thermus lineage has lost a set of genes that are still present in Deinococcus and many other mesophilic bacteria but are not common among thermophiles. By contrast, Deinococcus seems to have acquired numerous genes related to stress response systems from various bacteria. A comparison of the distribution of orthologous genes among the four partitions of the Deinococcus genome and the two partitions of the Thermus genome reveals homology between the Thermus megaplasmid (pTT27) and Deinococcus megaplasmid (DR177). CONCLUSION: After the radiation from their common ancestor, the Thermus and Deinococcus lineages have taken divergent paths toward their distinct lifestyles. In addition to extensive gene loss, Thermus seems to have acquired numerous genes from thermophiles, which likely was the decisive contribution to its thermophilic adaptation. By contrast, Deinococcus lost few genes but seems to have acquired many bacterial genes that apparently enhanced its ability to survive different kinds of environmental stresses. Notwithstanding the accumulation of horizontally transferred genes, we also show that the single megaplasmid of Thermus and the DR177 megaplasmid of Deinococcus are homologous and probably were inherited from the common ancestor of these bacteria

Evolution of AANAT: expansion of the gene family in the cephalochordate amphioxus

<p>Abstract</p> <p>Background</p> <p>The arylalkylamine <it>N</it>-acetyltransferase (AANAT) family is divided into structurally distinct vertebrate and non-vertebrate groups. Expression of vertebrate AANATs is limited primarily to the pineal gland and retina, where it plays a role in controlling the circadian rhythm in melatonin synthesis. Based on the role melatonin plays in biological timing, AANAT has been given the moniker "the Timezyme". Non-vertebrate AANATs, which occur in fungi and protists, are thought to play a role in detoxification and are not known to be associated with a specific tissue.</p> <p>Results</p> <p>We have found that the amphioxus genome contains seven <it>AANAT</it>s, all having non-vertebrate type features. This and the absence of <it>AANATs </it>from the genomes of Hemichordates and Urochordates support the view that a major transition in the evolution of the <it>AANATs </it>may have occurred at the onset of vertebrate evolution. Analysis of the expression pattern of the two most structurally divergent <it>AANAT</it>s in <it>Branchiostoma lanceolatum </it>(<it>bl</it>) revealed that they are expressed early in development and also in the adult at low levels throughout the body, possibly associated with the neural tube. Expression is clearly not exclusively associated with the proposed analogs of the pineal gland and retina. blAANAT activity is influenced by environmental lighting, but light/dark differences do not persist under constant light or constant dark conditions, indicating they are not circadian in nature. bfAANATα and bfAANATδ' have unusually alkaline (> 9.0) optimal pH, more than two pH units higher than that of vertebrate AANATs.</p> <p>Conclusions</p> <p>The substrate selectivity profiles of bfAANATα and δ' are relatively broad, including alkylamines, arylalkylamines and diamines, in contrast to vertebrate forms, which selectively acetylate serotonin and other arylalkylamines. Based on these features, it appears that amphioxus AANATs could play several roles, including detoxification and biogenic amine inactivation. The presence of seven AANATs in amphioxus genome supports the view that arylalkylamine and polyamine acetylation is important to the biology of this organism and that these genes evolved in response to specific pressures related to requirements for amine acetylation.</p

Complete genome sequence of the extremely acidophilic methanotroph isolate V4, Methylacidiphilum infernorum, a representative of the bacterial phylum Verrucomicrobia

<p>Abstract</p> <p>Background</p> <p>The phylum <it>Verrucomicrobia </it>is a widespread but poorly characterized bacterial clade. Although cultivation-independent approaches detect representatives of this phylum in a wide range of environments, including soils, seawater, hot springs and human gastrointestinal tract, only few have been isolated in pure culture. We have recently reported cultivation and initial characterization of an extremely acidophilic methanotrophic member of the <it>Verrucomicrobia</it>, strain V4, isolated from the Hell's Gate geothermal area in New Zealand. Similar organisms were independently isolated from geothermal systems in Italy and Russia.</p> <p>Results</p> <p>We report the complete genome sequence of strain V4, the first one from a representative of the <it>Verrucomicrobia</it>. Isolate V4, initially named "<it>Methylokorus infernorum</it>" (and recently renamed <it>Methylacidiphilum infernorum</it>) is an autotrophic bacterium with a streamlined genome of ~2.3 Mbp that encodes simple signal transduction pathways and has a limited potential for regulation of gene expression. Central metabolism of <it>M. infernorum </it>was reconstructed almost completely and revealed highly interconnected pathways of autotrophic central metabolism and modifications of C₁-utilization pathways compared to other known methylotrophs. The <it>M. infernorum </it>genome does not encode tubulin, which was previously discovered in bacteria of the genus <it>Prosthecobacter</it>, or close homologs of any other signature eukaryotic proteins. Phylogenetic analysis of ribosomal proteins and RNA polymerase subunits unequivocally supports grouping <it>Planctomycetes</it>, <it>Verrucomicrobia </it>and <it>Chlamydiae </it>into a single clade, the PVC superphylum, despite dramatically different gene content in members of these three groups. Comparative-genomic analysis suggests that evolution of the <it>M. infernorum </it>lineage involved extensive horizontal gene exchange with a variety of bacteria. The genome of <it>M. infernorum </it>shows apparent adaptations for existence under extremely acidic conditions including a major upward shift in the isoelectric points of proteins.</p> <p>Conclusion</p> <p>The results of genome analysis of <it>M. infernorum </it>support the monophyly of the PVC superphylum. <it>M. infernorum </it>possesses a streamlined genome but seems to have acquired numerous genes including those for enzymes of methylotrophic pathways <it>via </it>horizontal gene transfer, in particular, from <it>Proteobacteria</it>.</p> <p>Reviewers</p> <p>This article was reviewed by John A. Fuerst, Ludmila Chistoserdova, and Radhey S. Gupta.</p

Encapsulated in silica: genome, proteome and physiology of the thermophilic bacterium Anoxybacillus flavithermus WK1

Sequencing of the complete genome of Anoxybacillus flavithermus reveals enzymes that are required for silica adaptation and biofilm formation

Viral AlkB proteins repair RNA damage by oxidative demethylation

Bacterial and mammalian AlkB proteins are iron(II)- and 2-oxoglutarate-dependent dioxygenases that reverse methylation damage, such as 1-methyladenine and 3-methylcytosine, in RNA and DNA. An AlkB-domain is encoded by the genome of numerous single-stranded, plant-infecting RNA viruses, the majority of which belong to the Flexiviridae family. Our phylogenetic analysis of AlkB sequences suggests that a single plant virus might have acquired AlkB relatively recently, followed by horizontal dissemination among other viruses via recombination. Here, we describe the first functional characterization of AlkB proteins from three plant viruses. The viral AlkB proteins efficiently reactivated methylated bacteriophage genomes when expressed in Escherichia coli, and also displayed robust, iron(II)- and 2-oxoglutarate-dependent demethylase activity in vitro. Viral AlkB proteins preferred RNA over DNA substrates, and thus represent the first AlkBs with such substrate specificity. Our results suggest a role for viral AlkBs in maintaining the integrity of the viral RNA genome through repair of deleterious methylation damage, and support the notion that AlkB-mediated RNA repair is biologically relevant

Bioinformatics and functional analysis define four distinct groups of AlkB DNA-dioxygenases in bacteria

The iron(II)- and 2-oxoglutarate (2OG)-dependent dioxygenase AlkB from Escherichia coli (EcAlkB) repairs alkylation damage in DNA by direct reversal. EcAlkB substrates include methylated bases, such as 1-methyladenine (m1A) and 3-methylcytosine (m3C), as well as certain bulkier lesions, for example the exocyclic adduct 1,N6-ethenoadenine (εA). EcAlkB is the only bacterial AlkB protein characterized to date, and we here present an extensive bioinformatics and functional analysis of bacterial AlkB proteins. Based on sequence phylogeny, we show that these proteins can be subdivided into four groups: denoted 1A, 1B, 2A and 2B; each characterized by the presence of specific conserved amino acid residues in the putative nucleotide-recognizing domain. A scattered distribution of AlkB proteins from the four different groups across the bacterial kingdom indicates a substantial degree of horizontal transfer of AlkB genes. DNA repair activity was associated with all tested recombinant AlkB proteins. Notably, both a group 2B protein from Xanthomonas campestris and a group 2A protein from Rhizobium etli repaired etheno adducts, but had negligible activity on methylated bases. Our data indicate that the majority, if not all, of the bacterial AlkB proteins are DNA repair enzymes, and that some of these proteins do not primarily target methylated bases

Deinococcus geothermalis: The Pool of Extreme Radiation Resistance Genes Shrinks

Bacteria of the genus Deinococcus are extremely resistant to ionizing radiation (IR), ultraviolet light (UV) and desiccation. The mesophile Deinococcus radiodurans was the first member of this group whose genome was completely sequenced. Analysis of the genome sequence of D. radiodurans, however, failed to identify unique DNA repair systems. To further delineate the genes underlying the resistance phenotypes, we report the whole-genome sequence of a second Deinococcus species, the thermophile Deinococcus geothermalis, which at its optimal growth temperature is as resistant to IR, UV and desiccation as D. radiodurans, and a comparative analysis of the two Deinococcus genomes. Many D. radiodurans genes previously implicated in resistance, but for which no sensitive phenotype was observed upon disruption, are absent in D. geothermalis. In contrast, most D. radiodurans genes whose mutants displayed a radiation-sensitive phenotype in D. radiodurans are conserved in D. geothermalis. Supporting the existence of a Deinococcus radiation response regulon, a common palindromic DNA motif was identified in a conserved set of genes associated with resistance, and a dedicated transcriptional regulator was predicted. We present the case that these two species evolved essentially the same diverse set of gene families, and that the extreme stress-resistance phenotypes of the Deinococcus lineage emerged progressively by amassing cell-cleaning systems from different sources, but not by acquisition of novel DNA repair systems. Our reconstruction of the genomic evolution of the Deinococcus-Thermus phylum indicates that the corresponding set of enzymes proliferated mainly in the common ancestor of Deinococcus. Results of the comparative analysis weaken the arguments for a role of higher-order chromosome alignment structures in resistance; more clearly define and substantially revise downward the number of uncharacterized genes that might participate in DNA repair and contribute to resistance; and strengthen the case for a role in survival of systems involved in manganese and iron homeostasis