Convergent evolution of the arginine deiminase pathway:the ArcD and ArcE arginine/ornithine exchangers

The arginine deiminase (ADI) pathway converts L-arginine into L-ornithine and yields 1 mol of ATP per mol of L-arginine consumed. The L-arginine/L-ornithine exchanger in the pathway takes up L-arginine and excretes L-ornithine from the cytoplasm. Analysis of the genomes of 1281 bacterial species revealed the presence of 124 arc gene clusters encoding the pathway. About half of the clusters contained the gene encoding the well-studied L-arginine/L-ornithine exchanger ArcD, while the other half contained a gene, termed here arcE, encoding a membrane protein that is not a homolog of ArcD. The arcE gene product of Streptococcus pneumoniae was shown to take up L-arginine and L-ornithine with affinities of 0.6 and 1 μmol/L, respectively, and to catalyze metabolic energy-independent, electroneutral exchange. ArcE of S. pneumoniae could replace ArcD in the ADI pathway of Lactococcus lactis and provided the cells with a growth advantage. In contrast to ArcD, ArcE catalyzed translocation of the pathway intermediate L-citrulline with high efficiency. A short version of the ADI pathway is proposed for L-citrulline catabolism and the presence of the evolutionary unrelated arcD and arcE genes in different organisms is discussed in the context of the evolution of the ADI pathway

Family resemblances: A common fold for some dimeric ion-coupled secondary transporters

Membrane transporter proteins catalyze the passage of a broad range of solutes across cell membranes, allowing the uptake and efflux of crucial compounds. Because of the difficulty of expressing, purifying, and crystallizing integral membrane proteins, relatively few transporter structures have been elucidated to date. Although every membrane transporter has unique characteristics, structural and mechanistic similarities between evolutionarily diverse transporters have been identified. Here, we compare two recently reported structures of membrane proteins that act as antimicrobial efflux pumps, namely MtrF from Neisseria gonorrhoeae and YdaH from Alcanivorax borkumensis, both with each other and with the previously published structure of a sodium-dependent dicarboxylate transporter from Vibrio cholerae, VcINDY. MtrF and YdaH belong to the p-aminobenzoyl-glutamate transporter (AbgT) family and have been reported as having architectures distinct from those of all other families of transporters. However, our comparative analysis reveals a similar structural arrangement in all three proteins, with highly conserved secondary structure elements. Despite their differences in biological function, the overall "design principle" of MtrF and YdaH appears to be almost identical to that of VcINDY, with a dimeric quaternary structure, helical hairpins, and clear boundaries between the transport and scaffold domains. This observation demonstrates once more that the same secondary transporter architecture can be exploited for multiple distinct transport modes, including cotransport and antiport. Based on our comparisons, we detected conserved motifs in the substrate-binding region and predict specific residues likely to be involved in cation or substrate binding. These findings should prove useful for the future characterization of the transport mechanisms of these families of secondary active transporters

The bacterial dicarboxylate transporter VcINDY uses a two-domain elevator-type mechanism

Secondary transporters use alternating-access mechanisms to couple uphill substrate movement to downhill ion flux. Most known transporters use a 'rocking bundle' motion, wherein the protein moves around an immobile substrate-binding site. However, the glutamate-transporter homolog GltPh translocates its substrate-binding site vertically across the membrane, through an 'elevator' mechanism. Here, we used the 'repeat swap' approach to computationally predict the outward-facing state of the Na(+)/succinate transporter VcINDY, from Vibrio cholerae. Our model predicts a substantial elevator-like movement of VcINDY's substrate-binding site, with a vertical translation of ~15 Å and a rotation of ~43°. Our observation that multiple disulfide cross-links completely inhibit transport provides experimental confirmation of the model and demonstrates that such movement is essential. In contrast, cross-links across the VcINDY dimer interface preserve transport, thus revealing an absence of large-scale coupling between protomers

Factores protectores frente al consumo de alcohol: concepción de maestros de nivel inicial Fatores protetores frente ao consumo de álcool: percepção de professores de educação básica Protection factors against alcohol consumption as perceived by basic education teachers

Esta investigación busca comprender la concepción de maestros de nivel inicial sobre los factores protectores frente al consumo de alcohol, basándose en los modelos teóricos de Resiliencia y Promoción de la Salud. De enfoque metodológico cualitativo, exploratorio, aplica entrevistas semi-estructuradas y observación no estructurada a una muestra de 25 maestras. Del análisis de contenido de los datos surgen tres categorías temáticas: Significado de Alcohol/Alcoholismo - interpretado como sustancia nociva y situación problema socio-cultural -; La Escuela como Espacio de Protección Frente al Consumo de Alcohol; El Maestro como Agente de Protección. Se asocia protección con informar hasta cuidar. El maestro entiende su función desde orientador hasta consejero/protector, para la cual, mayoritariamente, no se siente preparado fundamentándose en déficits psicopedagógicos, cognocistivos, jurídico-legales y por propios prejuicios sobre alcoholismo. Los resultados confirman los presupuestos de la investigación relativos al maestro y contexto escolar.<br>O objetivo desta pesquisa é entender a percepção de professores de educação básica sobre os fatores que protegem contra o consumo de álcool. Foi adotada uma metodologia qualitativa do tipo exploratório, com entrevistas semi-estruturadas e observação não-estruturada aplicadas a uma amostra de 25 professoras. A análise de conteúdo dos dados levantou três categorias temáticas: Significado de Álcool/Alcoolismo; A Escola como Espaço de Proteção contra o Consumo de Álcool; o Professor como Agente de Proteção. O primeiro é interpretado como uma substância nociva e uma situação problema sócio-cultural. A proteção é associada com informar, comunicar, educar, ou cuidar. Portanto, o professor compreende sua função como cobrindo desde orientador até conselheiro ou protetor. A maioria não se sente preparada para desempenhá-la, fundamentando-se em déficits psicopedagógicos, conhecimentos de saúde integral, o arcabouço jurídico-legal e, principalmente, seus próprios preconceitos sobre alcoolismo.<br>This research aims to understand how basic education teachers perceive factors that protect against alcohol consumption. An exploratory qualitative methodological approach is adopted. Semi-structured interviews and non-structured observation techniques are applied to a sample of 25 teachers. Content analysis of data gave rise to three thematic categories: the Meaning of Alcohol/Alcoholism; The School as an Area of Protection against Alcohol Consumption; the Teacher as a Protective Agent. The first one is interpreted as a harmful substance and a sociocultural problem situation. Protection is linked up with informing, communicating, educating or caring. Thus, the way teachers see their function ranges from guide to adviser or protector. Most teachers do not feel prepared for it, on the basis of psychopedagogical deficits, integral health knowledge, the legal framework and, mainly, their own prejudices on alcoholism