Biological iron-sulfur storage in a thioferrateprotein nanoparticle

Iron-sulfur clusters are ubiquitous in biology and function in electron transfer and catalysis. They are assembled from iron and cysteine sulfur on protein scaffolds. Iron is typically stored as iron oxyhydroxide, ferrihydrite, encapsulated in 12 nm shells of ferritin, which buffers cellular iron availability. Here we have characterized IssA, a protein that stores iron and sulfur as thioferrate, an inorganic anionic polymer previously unknown in biology. IssA forms nanoparticles reaching 300 nm in diameter and is the largest natural metalloprotein complex known. It is a member of a widely distributed protein family that includes nitrogenase maturation factors, NifB and NifX. IssA nanoparticles are visible by electron microscopy as electron-dense bodies in the cytoplasm. Purified nanoparticles appear to be generated from 20 nm units containing ~6,400 Fe atoms and ~170 IssA monomers. In support of roles in both iron-sulfur storage and cluster biosynthesis, IssA reconstitutes the [4Fe-4S] cluster in ferredoxin in vitro

Emergent relations in pigeons following training with temporal samples

In two experiments, we investigated emergent conditional relations in pigeons using a symbolic matching-to-sample task with temporal stimuli as the samples and hues as the comparisons. Both experiments comprised three phases. In Phase I, pigeons learned to choose a red keylight (R) but not a green keylight (G) after a 1-s signal. They also learned to choose G but not R after a 4-s signal. In Phase II, correct responding consisted of choosing a blue keylight (B) after a 4-s signal and a yellow keylight (Y) after a 16-s signal. Comparisons G and B were both related to the same 4-s sample, whereas comparisons R and Y had no common sample. In Phase III, R and G were presented as samples, and B and Y were presented as the comparisons. The choice of B was correct following G, and the choice of Y was correct following R. If a relation between comparisons that shared a common sample were to emerge, then responding to B given G would be more likely than responding to Y given R. The results were generally consistent with this prediction, suggesting, for the first time in pigeons, the emergence of novel relations that involve temporal stimuli as nodal samples.This research was supported by doctoral grants to E.M.H. (FAPESP 60678-4/05 and CAPES 0103/08 0) and S.M.V. (CNPq 142544/2005-1 and CAPES 4457 07 2). G.Y.T. and D.G.d.S. were supported by a research productivity fellowship from The National Council for Scientific and Technological Development (CNPq, Brazil). A.D.M. was funded by the Portuguese Foundation for Science and Technology (FCT). All of the Brazilian authors are currently affiliated with the National Institute of Science and Technology on Behavior, Cognition and Teaching, supported by FAPESP (Grant No. 08/57705-8) and CNPq (Grant No. 573972/2008-7). The data were collected in the Animal Learning and Behavior Laboratory, University of Minho, Portugal, and were presented at the 36th Annual Meeting of the Brazilian Society of Psychology (SBP), Goiania, Brazil, in October 2009. E.M.H. is currently a college professor at the Universidade Federal de Minas Gerais.info:eu-repo/semantics/publishedVersio