New Structural and Functional Contexts of the Dx[DN]xDG Linear Motif: Insights into Evolution of Calcium-Binding Proteins

Binding of calcium ions (Ca2+) to proteins can have profound effects on their structure and function. Common roles of calcium binding include structure stabilization and regulation of activity. It is known that diverse families – EF-hands being one of at least twelve – use a Dx[DN]xDG linear motif to bind calcium in near-identical fashion. Here, four novel structural contexts for the motif are described. Existing experimental data for one of them, a thermophilic archaeal subtilisin, demonstrate for the first time a role for Dx[DN]xDG-bound calcium in protein folding. An integrin-like embedding of the motif in the blade of a β-propeller fold – here named the calcium blade – is discovered in structures of bacterial and fungal proteins. Furthermore, sensitive database searches suggest a common origin for the calcium blade in β-propeller structures of different sizes and a pan-kingdom distribution of these proteins. Factors favouring the multiple convergent evolution of the motif appear to include its general Asp-richness, the regular spacing of the Asp residues and the fact that change of Asp into Gly and vice versa can occur though a single nucleotide change. Among the known structural contexts for the Dx[DN]xDG motif, only the calcium blade and the EF-hand are currently found intracellularly in large numbers, perhaps because the higher extracellular concentration of Ca2+ allows for easier fixing of newly evolved motifs that have acquired useful functions. The analysis presented here will inform ongoing efforts toward prediction of similar calcium-binding motifs from sequence information alone

Brain Arachidonic Acid Incorporation and Turnover are not Altered in the Flinders Sensitive Line Rat Model of Human Depression

Brain serotonergic signaling is coupled to arachidonic acid (AA)-releasing calcium-dependent phospholipase A2. Increased brain serotonin concentrations and disturbed serotonergic neurotransmission have been reported in the Flinders Sensitive Line (FSL) rat model of depression, suggesting that brain AA metabolism may be elevated. To test this hypothesis, (14)C-AA was intravenously infused to steady-state levels into control and FSL rats derived from the same Sprague-Dawley background strain, and labeled and unlabeled brain phospholipid and plasma fatty acid concentrations were measured to determine the rate of brain AA incorporation and turnover. Brain AA incorporation and turnover did not differ significantly between controls and FSL rats. Compared to controls, plasma unesterified docosahexaenoic acid was increased, and brain phosphatidylinositol AA and total lipid linoleic acid and n-3 and n-6 docosapentaenoic acid were significantly decreased in FSL rats. Several plasma esterified fatty acids differed significantly from controls. In summary, brain AA metabolism did not change in FSL rats despite reported increased levels of serotonin concentrations, suggesting possible post-synaptic dampening of serotonergic neurotransmission involving AA

Bosques secundarios ?Manejarlos, preservarlos o eliminarlos?

Los bosques secundarios en Centroam?rica tienen un gran potencial socioecon?mico, no solo por su extensi?n en continuo crecimiento (por abandono de pasturas y suelos degradados), sino tambi?n por los beneficios que pueden brindar (similares a los de los bosques primarios e intervenidos pero con mejor accesibilidad pues anteriormente el uso del suelo estaba dedicado a la ganader?a y la agricultura). Pese a ello, el aprovechamiento de estos bosques se ve dificultado por un marco legal inadecuado y ausencia de normas espec?ficas para estos ecosistemas. Las iniciativas de manejo de estos bosques suelen entonces ser reguladas a partir de disposiciones definidas para bosques primarios, los cuales suelen ser muy diferentes en cuanto a comportamiento, composici?n y estructura y, por lo tanto, a sistemas de manejo forestal. Este vac?o legal desmotiva a los propietarios y los incita a eliminar la sucesi?n secundaria en sus predios, lo cual puede afectar seriamente la cobertura forestal en la regi?n revirtiendo ?reas ya recuperadas nuevamente al uso agr?cola y ganadero. Con el fin de promover el manejo y aprovechamiento de los bosques secundarios para mejorar su valor y viabilizar su conservaci?n y contribuci?n a la cobertura forestal en Centroam?rica, es importante establecer protocolos simplificados e incentivos adecuados que permitan a los propietarios manejar estos ecosistemas y mercadear legalmente sus productos y tener as? una opci?n adicional de ingresos

Metamorphic proteins mediate evolutionary transitions of structure

The primary sequence of proteins usually dictates a single tertiary and quaternary structure. However, certain proteins undergo reversible backbone rearrangements. Such metamorphic proteins provide a means of facilitating the evolution of new folds and architectures. However, because natural folds emerged at the early stages of evolution, the potential role of metamorphic intermediates in mediating evolutionary transitions of structure remains largely unexplored. We evolved a set of new proteins based on ∼100 amino acid fragments derived from tachylectin-2—a monomeric, 236 amino acids, five-bladed β-propeller. Their structures reveal a unique pentameric assembly and novel β-propeller structures. Although identical in sequence, the oligomeric subunits adopt two, or even three, different structures that together enable the pentameric assembly of two propellers connected via a small linker. Most of the subunits adopt a wild-type-like structure within individual five-bladed propellers. However, the bridging subunits exhibit domain swaps and asymmetric strand exchanges that allow them to complete the two propellers and connect them. Thus, the modular and metamorphic nature of these subunits enabled dramatic changes in tertiary and quaternary structure, while maintaining the lectin function. These oligomers therefore comprise putative intermediates via which β-propellers can evolve from smaller elements. Our data also suggest that the ability of one sequence to equilibrate between different structures can be evolutionary optimized, thus facilitating the emergence of new structures