Same/different concept learning by capuchin monkeys in matching-to-sample tasks

The ability to understand similarities and analogies is a fundamental aspect of human advanced cognition. Although subject of considerable research in comparative cognition, the extent to which nonhuman species are capable of analogical reasoning is still debated. This study examined the conditions under which tufted capuchin monkeys (Cebus apella) acquire a same/different concept in a matching-to-sample task on the basis of relational similarity among multi-item stimuli. We evaluated (i) the ability of five capuchin monkeys to learn the same/different concept on the basis of the number of items composing the stimuli and (ii) the ability to match novel stimuli after training with both several small stimulus sets and a large stimulus set. We found the first evidence of same/different relational matching-to-sample abilities in a New World monkey and demonstrated that the ability to match novel stimuli is within the capacity of this species. Therefore, analogical reasoning can emerge in monkeys under specific training conditions.     

Atomic structures suggest determinants of transmission barriers in mammalian prion disease

Prion represents a unique class of pathogens devoid of nucleic acid. The deadly diseases transmitted by it between members of one species and, in certain instances, to members of other species present a public health concern. Transmissibility and the barriers to transmission between species have been suggested to arise from the degree to which a pathological protein conformation from an individual of one species can seed a pathological conformation in another species. However, this hypothesis has never been illustrated at an atomic level. Here we present three X-ray atomic structures of the same segment from human, mouse, and hamster PrP, which is critical for forming amyloid and confers species specificity in PrP seeding experiments. The structures reveal that different sequences encode different steric zippers and suggest that the degree of dissimilarity of these zipper structures gives rise to transmission barriers in prion disease, such as those that protect humans from acquiring bovine spongiform encephalopathy (BSE) and chronic wasting disease (CWD).     

How does regulatory Ca2+ regulate the Na+-Ca2+ exchanger?

Spatial and temporal regulation of intracellular Ca2+ concentrations is a fundamental requirement for life. The mammalian cardiac Na+-Ca2+ exchanger serves as the main mechanism for Ca2+ efflux after heart contraction. Exchange activity is highly regulated by intracellular Ca2+, which binds two regulatory domains (CBD1 and CBD2) and triggers the full activity of the exchanger. We solved the X-ray crystallographic structure of CBD2 in the presence and absence of Ca2+. Together with mutational analysis of the Ca2+ binding sites, this study reveals the crucial role of one of the two bound Ca2+ ions and helps propose hypotheses on the mechanism of regulation of the exchanger.     

Thyrotropin regulation of membrane lipid fluidity in the FRTL-5 thyroid cell line. Its relationship to cell growth and functional activity

The mitogenic effect of thyrotropin on functional rat thyroid cells of the line FRTL-5 is correlated with membrane lipid fluidity as evaluated by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene. Continued exposure of FRTL-5 cells to a medium lacking thyrotropin causes cessation of cell proliferation and a decrease in membrane lipid fluidity which reaches its minimum in approximately 8 days. The change in lipid fluidity is due to an absolute increase (greater than 2-fold) of membrane cholesterol, with an increased cholesterol/phospholipid ratio and an increased ratio of saturated to unsaturated fatty acids of the membrane phospholipids, contributed primarily by a nearly 4-fold increase in the ratio of saturated to unsaturated C16 fatty acids. It is also associated with a variation of the relative proportions of the major membrane phospholipids; thus, phosphatidylinositol and phosphatidylethanolamine decrease while phosphatidylcholine increases. Both membrane fluidity and lipid composition can be restored by thyrotropin to their original levels, i.e. levels measured under continuous exposure to the hormone. Complete reversal requires at least 48 h, i.e. approximately the same time required for resumption of growth when FRTL-5 cells, starved in thyrotropin, are re-exposed to the hormone. Changes in lipid composition and fluidity can be prevented or can be reversed if FRTL-5 cells are exposed to dibutyryl cAMP while being deprived of thyrotropin. Dibutyryl cAMP has only a modest direct effect on growth; however, this pretreatment eliminates the 48-h lag phase with respect to thyrotropin stimulation. It is proposed that the effects of thyrotropin on growth of FRTL-5 cells requires a modification of the molecular structure and the physical state of cell membranes, which can be mediated by cAMP, although cAMP is not sufficient by itself to promote growth.     

Secretion of psychrophilic alpha-amylase deletion mutants in Pseudoalteromonas haloplanktis TAC125

The nature and location of structural features responsible for the secretion of a cold-adapted alpha-amylase in the Antarctic marine bacterium Pseudoalteromonas haloplanktis TAC125 was studied by deletion mutagenesis of the wild-type enzyme and of chimerical proteins derived from the fusion of the alpha-amylase with a reporter enzyme. Domain C of the psychrophilic alpha-amylase contains secretion features involved in extracellular targeting.     

Atomic structure of the cross-beta spine of islet amyloid polypeptide (amylin)

Human islet amyloid polypeptide (IAPP or amylin) is a 37-residue hormone found as fibrillar deposits in pancreatic extracts of nearly all type II diabetics. Although the cellular toxicity of IAPP has been established, the structure of the fibrillar form found in these deposits is unknown. Here we have crystallized two segments from IAPP, which themselves form amyloid-like fibrils. The atomic structures of these two segments, NNFGAIL and SSTNVG, were determined, and form the basis of a model for the most commonly observed, full-length IAPP polymorph.     

Structural and EPR characterization of the soluble form of cytochrome c-550 and of the psbV2 gene product from the cyanobacterium Thermosynechococcus elongatus

First, the crystal structure of cytochrome c-550 (the psbV1 gene product) from the thermophilic cyanobacterium Thermosynechococcus elongatus has been determined to a resolution of 1.8 A. A comparison of the T. elongatus cytochrome c-550 structure to its counterparts from mesophilic organisms, Synechocystis 6803 and Arthrospira maxima, suggests that increased numbers of hydrogen bonds may play a role in the structural basis of thermostability. The cytochrome c-550 in T. elongatus also differs from that in Synechocystis 6803 and Arthrospira maxima in its lack of dimerization and the presence of a trigonal planar molecule, possibly bicarbonate, tightly bound to the heme propionate oxygen atoms. Cytochromes c-550 from T. elongatus, Synechocystis 6803 and Arthrospira maxima exhibit different EPR spectra. A correlation has been done between the heme-axial ligands geometries and the rhombicity calculated from the EPR spectra. This correlation indicates that binding of cytochrome c-550 to Photosystem II is accompanied by structural changes in the heme vicinity. Second, the psbV2 gene product has been found and purified. The UV-visible, EPR and Raman spectra are reported. From the spectroscopic data and from a theoretical structural model based on the cytochrome c-550 structure it is proposed that the 6th ligand of the heme-iron is the Tyr86.