A census of membrane-bound and intracellular signal transduction proteins in bacteria: Bacterial IQ, extroverts and introverts

BACKGROUND: Analysis of complete microbial genomes showed that intracellular parasites and other microorganisms that inhabit stable ecological niches encode relatively primitive signaling systems, whereas environmental microorganisms typically have sophisticated systems of environmental sensing and signal transduction. RESULTS: This paper presents results of a comprehensive census of signal transduction proteins – histidine kinases, methyl-accepting chemotaxis receptors, Ser/Thr/Tyr protein kinases, adenylate and diguanylate cyclases and c-di-GMP phosphodiesterases – encoded in 167 bacterial and archaeal genomes, sequenced by the end of 2004. The data have been manually checked to avoid false-negative and false-positive hits that commonly arise during large-scale automated analyses and compared against other available resources. The census data show uneven distribution of most signaling proteins among bacterial and archaeal phyla. The total number of signal transduction proteins grows approximately as a square of genome size. While histidine kinases are found in representatives of all phyla and are distributed according to the power law, other signal transducers are abundant in certain phylogenetic groups but virtually absent in others. CONCLUSION: The complexity of signaling systems differs even among closely related organisms. Still, it usually can be correlated with the phylogenetic position of the organism, its lifestyle, and typical environmental challenges it encounters. The number of encoded signal transducers (or their fraction in the total protein set) can be used as a measure of the organism's ability to adapt to diverse conditions, the 'bacterial IQ', while the ratio of transmembrane receptors to intracellular sensors can be used to define whether the organism is an 'extrovert', actively sensing the environmental parameters, or an 'introvert', more concerned about its internal homeostasis. Some of the microorganisms with the highest IQ, including the current leader Wolinella succinogenes, are found among the poorly studied beta-, delta- and epsilon-proteobacteria. Among all bacterial phyla, only cyanobacteria appear to be true introverts, probably due to their capacity to conduct oxygenic photosynthesis, using a complex system of intracellular membranes. The census data, available at , can be used to get an insight into metabolic and behavioral propensities of each given organism and improve prediction of the organism's properties based solely on its genome sequence

The Molecular Biology Database Collection: 2007 update

The NAR online Molecular Biology Database Collection is a public resource that contains links to the databases described in this issue of Nucleic Acids Research, previous NAR database issues, as well as a selection of other molecular biology databases that are freely available on the web and might be useful to the molecular biologist. The 2007 update includes 968 databases, 110 more than the previous one. Many databases that have been described in earlier issues of NAR come with updated summaries, which reflect recent progress and, in some instances, an expanded scope of these databases. The complete database list and summaries are available online on the Nucleic Acids Research web site

The Molecular Biology Database Collection: 2006 update

The NAR Molecular Biology Database Collection is a public online resource that contains links to all databases described in this issue of Nucleic Acids Research. In addition, this collection lists databases that have been featured in previous issues of NAR, as well as selected other databases that are freely available to the public and may be useful to the molecular biologist. The 2006 update includes 858 databases, 139 more than the previous one. The databases come with brief summaries, many of which have been updated recently. Each database is assigned a stable accession number that does not change if the database moves to a new location and its URL, authors' names or the contact person address are updated. The complete database list and summaries are available online at the Nucleic Acids Research website

On the origin of life in the Zinc world. 2. Validation of the hypothesis on the photosynthesizing zinc sulfide edifices as cradles of life on Earth

<p>Abstract</p> <p>Background</p> <p>The accompanying article (A.Y. Mulkidjanian, <it>Biology Direct </it>4:26) puts forward a detailed hypothesis on the role of zinc sulfide (ZnS) in the origin of life on Earth. The hypothesis suggests that life emerged within compartmentalized, photosynthesizing ZnS formations of hydrothermal origin (the Zn world), assembled in sub-aerial settings on the surface of the primeval Earth.</p> <p>Results</p> <p>If life started within photosynthesizing ZnS compartments, it should have been able to evolve under the conditions of elevated levels of Zn²⁺ions, byproducts of the ZnS-mediated photosynthesis. Therefore, the Zn world hypothesis leads to a set of testable predictions regarding the specific roles of Zn²⁺ions in modern organisms, particularly in RNA and protein structures related to the procession of RNA and the "evolutionarily old" cellular functions. We checked these predictions using publicly available data and obtained evidence suggesting that the development of the primeval life forms up to the stage of the Last Universal Common Ancestor proceeded in zinc-rich settings. Testing of the hypothesis has revealed the possible supportive role of manganese sulfide in the primeval photosynthesis. In addition, we demonstrate the explanatory power of the Zn world concept by elucidating several points that so far remained without acceptable rationalization. In particular, this concept implies a new scenario for the separation of Bacteria and Archaea and the origin of Eukarya.</p> <p>Conclusion</p> <p>The ability of the Zn world hypothesis to generate non-trivial veritable predictions and explain previously obscure items gives credence to its key postulate that the development of the first life forms started within zinc-rich formations of hydrothermal origin and was driven by solar UV irradiation. This concept implies that the geochemical conditions conducive to the origin of life may have persisted only as long as the atmospheric CO₂pressure remained above ca. 10 bar. This work envisions the first Earth biotopes as photosynthesizing and habitable areas of porous ZnS and MnS precipitates around primeval hot springs. Further work will be needed to provide details on the life within these communities and to elucidate the primordial (bio)chemical reactions.</p> <p>Reviewers</p> <p>This article was reviewed by Arcady Mushegian, Eugene Koonin, and Patrick Forterre. For the full reviews, please go to the Reviewers' reports section.</p

Survival of the fittest before the beginning of life: selection of the first oligonucleotide-like polymers by UV light

BACKGROUND: A key event in the origin of life on this planet has been formation of self-replicating RNA-type molecules, which were complex enough to undergo a Darwinian-type evolution (origin of the "RNA world"). However, so far there has been no explanation of how the first RNA-like biopolymers could originate and survive on the primordial Earth. RESULTS: As condensation of sugar phosphates and nitrogenous bases is thermodynamically unfavorable, these compounds, if ever formed, should have undergone rapid hydrolysis. Thus, formation of oligonucleotide-like structures could have happened only if and when these structures had some selective advantage over simpler compounds. It is well known that nitrogenous bases are powerful quenchers of UV quanta and effectively protect the pentose-phosphate backbones of RNA and DNA from UV cleavage. To check if such a protection could play a role in abiogenic evolution on the primordial Earth (in the absence of the UV-protecting ozone layer), we simulated, by using Monte Carlo approach, the formation of the first oligonucleotides under continuous UV illumination. The simulations confirmed that UV irradiation could have worked as a selective factor leading to a relative enrichment of the system in longer sugar-phosphate polymers carrying nitrogenous bases as UV-protectors. Partial funneling of the UV energy into the condensation reactions could provide a further boost for the oligomerization. CONCLUSION: These results suggest that accumulation of the first polynucleotides could be explained by their abiogenic selection as the most UV-resistant biopolymers

Conserved ‘Hypothetical’ Proteins: New Hints and New Puzzles

Conserved hypothetical proteins, i.e. conserved proteins whose functions are still unknown, pose a challenge not just to functional genomics but also to general biology. For many conserved proteins, computational analysis provides only a general prediction of biochemical function; their exact biological functions have to be established through direct experimentation. In the few cases when this has been accomplished, the results were remarkable, revealing the deoxyxylulose pathway and a new essential enzyme, the ITP pyrophosphatase. Comparative genome analysis is also instrumental in illuminating unsolved problems in biology, e.g. the mechanism of FtsZ-independent cell division in Chlamydia, Ureaplasma and Aeropyrum or the role of uncharacterized conserved domains in signal transduction

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