ABSTRACT
The five-membered heterocyclic imidazole group, which is an essential component of purines, histidine and many cofactors, has been abiotically synthesized in different model experiments that attempt to simulate the prebiotic environment. The evolutionary significance of imidazoles is highlighted not only by its presence in nucleic acid components and in histidine, but also by experimental reports of its ability to restore the catalytic activity of ribozymes. However, as of today there are no reports of histidine in carbonaceous chondrites, and although the abiotic synthesis of His reported by Shen et al. (1987, 1990a) proceeds via an Amadori rearrangement, like in the biosynthesis of histidine, neither the reactants nor the conditions are truly prebiotic. Based on the autocatalytic biosynthesis of 4-methylidene-imidazole-one (MIO), a cofactor of some members of the amino acid aromatic ammonia-lyases and aminomutases, which occur via the self-condensation of a simple Ala-Ser-Gly motif within the sequence of the enzymes, we propose a possible prebiotic synthesis of an imidazolide.
Subject(s)
Evolution, Chemical , Imidazoles/chemistry , Origin of LifeABSTRACT
Azospirillum brasilense is a nitrogen-fixing bacterium living in association with plant roots. The genome of the strain Sp245, isolated in Brazil from wheat roots, consists of one chromosome and six plasmids. In this work, the A. brasilense Sp245 plasmids were analyzed in order to shed some light on the evolutionary pathways they followed over time. To this purpose, a similarity network approach was applied in order to identify the evolutionary relationships among all the A. brasilense plasmids encoded proteins; in this context a computational pipeline specifically devoted to the analysis and the visualization of the network-like evolutionary relationships among different plasmids molecules was developed. This information was supplemented with a detailed (in silico) functional characterization of both the connected (i.e., sharing homology with other sequences in the dataset) and the unconnected (i.e., not sharing homology) components of the network. Furthermore, the most likely source organism for each of the genes encoded by A. brasilense plasmids was checked, allowing the identification of possible trends of gene loss/gain in this microorganism. Data obtained provided a detailed description of the evolutionary landscape of the plasmids of A. brasilense Sp245, suggesting some of the molecular mechanisms responsible for the present-day structure of these molecules.
ABSTRACT
Os autores abordam o comportamento da hepatite viral durante o ciclo grávido-puerperal, por ser a maior causa de icterícia neste período. Confirmam a importância da transmissão vertical para a hepatite do tipo B, além de sinalizarem para a gravidade da hepatite dos tipos C e E. O tipo C tem altas taxas de cronificação e o tipo E, quando adquirido no terceiro trimestre da gestação, apresenta a possibilidade de hepatite fulminante, com morte materna. Relembram o diagnóstico clássico da fase aguda e a assintomática fase crônica, além de lembrarem os possíveis diagnósticos diferenciais. A literatura é unânime em recomendar o rastreamento universal para a hepatite B, deixando as demais formas para situações de forte evidência epidemiológica. Finalmente informam as possibilidades terapêuticas com imunoglobulinas aplicadas na mãe e no recém-nato