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Metazoan innovation: from aromatic amino acids to extracellular signaling.

ABSTRACT: Tyrosine depletion in metazoan proteins was recently explained to be due to the appearance of tyrosine kinases in Metazoa. Here, we present a complementary explanation for the depletion of tyrosine, stating the importance of tyrosine in signaling not only as a phosphorylation target but also as a precursor for catecholamines and hormones. Molecules (dopamine, norepinephrine, and epinephrine, and to a lesser extent serotonin and melatonin) critical to metazoan multicellular signaling are also greatly dependent on a supply of tyrosine. These signaling molecules are synthesized in two highly linked pathways specific to metazoans. In addition, the shikimate pathway that non-metazoans use to synthesize the aromatic amino acids is not present in metazoans. These important pathway changes have occurred between Metazoa and other eukaryotes, causing significant changes to tyrosine metabolism and rendering tyrosine crucial for extracellular signaling. In addition, the evolutionary and functional linkage between these two pathways and the resulting implications for neuropathology are discussed.

SUBMITTER: Kutchko KM

PROVIDER: S-EPMC3716840 | biostudies-literature | 2013 Aug

REPOSITORIES: biostudies-literature

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Metazoan innovation: from aromatic amino acids to extracellular signaling.

Kutchko Katrina M KM Siltberg-Liberles Jessica J

Amino acids 20130521 2

Tyrosine depletion in metazoan proteins was recently explained to be due to the appearance of tyrosine kinases in Metazoa. Here, we present a complementary explanation for the depletion of tyrosine, stating the importance of tyrosine in signaling not only as a phosphorylation target but also as a precursor for catecholamines and hormones. Molecules (dopamine, norepinephrine, and epinephrine, and to a lesser extent serotonin and melatonin) critical to metazoan multicellular signaling are also gre ...[more]

PMID: 23690137

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Project description:UnlabelledIt has been proposed that Geobacter sulfurreducens requires conductive pili for long-range electron transport to Fe(III) oxides and for high-density current production in microbial fuel cells. In order to investigate this further, we constructed a strain of G. sulfurreducens, designated Aro-5, which produced pili with diminished conductivity. This was accomplished by modifying the amino acid sequence of PilA, the structural pilin protein. An alanine was substituted for each of the five aromatic amino acids in the carboxyl terminus of PilA, the region in which G. sulfurreducens PilA differs most significantly from the PilAs of microorganisms incapable of long-range extracellular electron transport. Strain Aro-5 produced pili that were properly decorated with the multiheme c-type cytochrome OmcS, which is essential for Fe(III) oxide reduction. However, pili preparations of the Aro-5 strain had greatly diminished conductivity and Aro-5 cultures were severely limited in their capacity to reduce Fe(III) compared to the control strain. Current production of the Aro-5 strain, with a graphite anode serving as the electron acceptor, was less than 10% of that of the control strain. The conductivity of the Aro-5 biofilms was 10-fold lower than the control strain's. These results demonstrate that the pili of G. sulfurreducens must be conductive in order for the cells to be effective in extracellular long-range electron transport.ImportanceExtracellular electron transfer by Geobacter species plays an important role in the biogeochemistry of soils and sediments and has a number of bioenergy applications. For example, microbial reduction of Fe(III) oxide is one of the most geochemically significant processes in anaerobic soils, aquatic sediments, and aquifers, and Geobacter organisms are often abundant in such environments. Geobacter sulfurreducens produces the highest current densities of any known pure culture, and close relatives are often the most abundant organisms colonizing anodes in microbial fuel cells that harvest electricity from wastewater or aquatic sediments. The finding that a strain of G. sulfurreducens that produces pili with low conductivity is limited in these extracellular electron transport functions provides further insight into these environmentally significant processes.

Project description:Pseudomonas putida is a highly solvent-resistant microorganism and useful chassis for the production of value-added compounds from lignocellulosic residues, in particular aromatic compounds that are made from phenylalanine. The use of these agricultural residues requires a two-step treatment to release the components of the polysaccharides of cellulose and hemicellulose as monomeric sugars, the most abundant monomers being glucose and xylose. Pan-genomic studies have shown that Pseudomonas putida metabolizes glucose through three convergent pathways to yield 6-phosphogluconate and subsequently metabolizes it through the Entner-Doudoroff pathway, but the strains do not degrade xylose. The valorization of both sugars is critical from the point of view of economic viability of the process. For this reason, a P. putida strain was endowed with the ability to metabolize xylose via the xylose isomerase pathway, by incorporating heterologous catabolic genes that convert this C5 sugar into intermediates of the pentose phosphate cycle. In addition, the open reading frame T1E_2822, encoding glucose dehydrogenase, was knocked-out to avoid the production of the dead-end product xylonate. We generated a set of DOT-T1E-derived strains that metabolized glucose and xylose simultaneously in culture medium and that reached high cell density with generation times of around 100 min with glucose and around 300 min with xylose. The strains grew in 2G hydrolysates from diluted acid and steam explosion pretreated corn stover and sugarcane straw. During growth, the strains metabolized > 98% of glucose, > 96% xylose and > 85% acetic acid. In 2G hydrolysates P. putida 5PL, a DOT-T1E derivative strain that carries up to five independent mutations to avoid phenylalanine metabolism, accumulated this amino acid in the medium. We constructed P. putida 5PLΔgcd (xylABE) that produced up to 250 mg l-1 of phenylalanine when grown in 2G pretreated corn stover or sugarcane straw. These results support as a proof of concept the potential of P. putida as a chassis for 2G processes.

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Metazoan innovation: from aromatic amino acids to extracellular signaling.

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Metazoan innovation: from aromatic amino acids to extracellular signaling.

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