Structural basis for α-conotoxin potency and selectivity

Parkinson’s disease is a debilitating movement disorder characterized by altered levels of α₆β₂1 (1 indicates the possible presence of additional subunits) nicotinic acetylcholine receptors (nAChRs) localized on presynaptic striatal catecholaminergic neurons. α-Conotoxin MII (α-CTx MII) is a highly useful ligand to probe α₆β₂ nAChRs structure and function, but it does not discriminate among closely related α₆1 nAChR subtypes. Modification of the α-CTx MII primary sequence led to the identification of α-CTx MII[E11A], an analog with 500–5300-fold discrimination between α₆1 subtypes found in both human and non-human primates. α-CTx MII[E11A] binds most strongly (femtomolar dissociation constant) to the high affinity α₆ nAChR, a subtype that is selectively lost in Parkinson’s disease. Here, we present the three-dimensional solution structure for α-CTx MII[E11A] as determined by two-dimensional ¹H NMR spectroscopy to 0.13 ± 0.09 ? backbone and 0.45 ± 0.08 ? heavy atom root-mean-square deviation from mean structure. Structural comparisons suggest that the increased hydrophobic area of α-CTx MII[E11A] relative to other members of the α-CTx family may be responsible for its exceptionally high affinity for α6α4β21 nAChR as well as discrimination between α₆β₂ and α₃β₂ containing nAChRs. This finding may enable the rational design of novel peptide analogs that demonstrate enhanced specificity for α₆1 nAChR subunit interfaces and provide a means to better understand nAChR structural determinants that modulate brain dopamine levels and the pathophysiology of Parkinson’s disease.     

The Effects of Artificial Beach Nourishment on Marine Turtles: Differences between Loggerhead and Green Turtles

Marine turtle reproductive success is correlated with the stability and quality of the nesting environment. Female marine turtles show fidelity to nesting beaches, making artificial beach nourishment practices directly relevant to their recovery. We evaluated the impacts of artificial beach nourishment on Loggerhead ( Caretta caretta ) and Green turtles ( Chelonia mydas ) between artificially nourished and nonnourished beaches. We observed reduced nesting success (ratio of nesting emergences to emergences not resulting in nest deposition) for both species. This negative effect lasted for one season in Loggerheads and for at least one season in Green turtles. Physical attributes of the fill sand did not impede nesting attempts. We argue that the decrease in nesting success resulted from an altered beach profile not favorable for nest deposition, which subsequently improved in later seasons as the beach equilibrated to a more natural slope. We observed a 52.2% decrease in reproductive output (hatchlings km⁻¹ yr⁻¹) for Loggerheads one year postnourishment, with a 44.1% increase observed the two seasons postnourishment. In Green turtles, a 0.8% reduction was observed the first season postnourishment, despite a 13% increase in the nonnourished area. The reduction in reproductive output in both cases was primarily a consequence of decreased nesting success, lowering nest numbers. These results reveal stronger negative effects of beach nourishment on Loggerheads compared to Green turtles and the importance of minimizing excessive nonnesting emergences associated with artificial beach nourishment. Nourished areas also experienced more than 600% increase in the number of Loggerhead hatchlings disoriented by artificial lighting over two years postnourishment.     

A case study of human exacerbation of the invasive species problem: transport and establishment of polygyne fire ants in Tallahassee, Florida, USA

Understanding how exotic invasive species are spread is fundamental for ecology and conservation biology. Human transport has become one of the primary modes of dispersal for exotic species. We examined how the multiple queen, or polygyne, social form of the fire ant Solenopsis invicta is spread along roadsides in Tallahassee, Florida, USA. We then determined the likely source of this expanding population, which was a central soil depot. A survey of road maintenance practices in counties of several southeastern states and Texas revealed that the use of a central soil depot is a common practice. Road maintenance therefore may be the primary source for the establishment of new polygyne fire ant populations in this region and elsewhere. Control efforts focused on the soil depots will help to limit further spread of polygyne fire ants and perhaps other invasive organisms, particularly invasive weeds.     

Towards a physical description of habitat: quantifying environmental adversity (abiotic stress) in temperate forest and woodland ecosystems

1. Our aim was to develop a quantitative proxy for environmental adversity (abiotic stress) in temperate Eucalyptus and Nothofagus forest and woodland ecosystems.
2. Samples and measurements were collected at 42 sites across a rainfall gradient in southern Australia, an elevation gradient in south-eastern Australia, and a longitudinal transect (temperature gradient) in Patagonia, Argentina.
3. We compared the ability of (a) abiotic variables (14 soil and 21 climatic variables) and (b) the stable carbon isotope (δ¹³C) values of soil organic matter (SOM), to predict variation in leaf area index (LAI; a forest productivity variable).
4. The δ¹³C of SOM (soil aggregates) explained more variation (57%) in LAI than multivariate statistical models that integrated information on many abiotic variables. W* (a climatic water balance model) was also a powerful predictor variable, explaining 37% of the variability in LAI.
5 Synthesis . The stable carbon isotopic signature of soil aggregates is a powerful explanatory variable that may help us to quantify environmental adversity (abiotic stress) in temperate forest and woodland ecosystems.     

Role of Allosteric Switch Residue Histidine 195 in Maintaining Active-Site Asymmetry in Presynaptic Filaments of Bacteriophage T4 UvsX Recombinase

Cyanophycin, or poly-l-Asp-multi-l-Arg, is a non-ribosomally synthesized peptidic polymer that is used for nitrogen storage by cyanobacteria and other select eubacteria. Upon synthesis, it self-associates to form insoluble granules, the degradation of which is uniquely catalyzed by a carboxy-terminal-specific protease, cyanophycinase. We have determined the structure of cyanophycinase from the freshwater cyanobacterium Synechocystis sp. PCC6803 at 1.5-Å resolution, showing that the structure is dimeric, with individual protomers resembling aspartyl dipeptidase. Kinetic characterization of the enzyme demonstrates that the enzyme displays Michaelis-Menten kinetics with a k_cat of 16.5 s^− 1 and a k_cat/K_M of 7.5 × 10^− 6 M^− 1 s^− 1. Site-directed mutagenesis experiments confirm that cyanophycinase is a serine protease and that Gln101, Asp172, Gln173, Arg178, Arg180 and Arg183, which form a conserved pocket adjacent to the catalytic Ser132, are functionally critical residues. Modeling indicates that cyanophycinase binds the β-Asp-Arg dipeptide residue immediately N-terminal to the scissile bond in an extended conformation in this pocket, primarily recognizing this penultimate β-Asp-Arg residue of the polymeric chain. Because binding and catalysis depend on substrate features unique to β-linked aspartyl peptides, cyanophycinase is able to act within the cytosol without non-specific cleavage events disrupting essential cellular processes.     

Sulfate Activation Enzymes: Phylogeny and Association with Pyrophosphatase

The enzymes catalyzing the first two reactions in the sulfate activation pathway, ATP-sulfurylase (S) and APS-kinase (K), are fused as ‘KS’ in animals but are fused as ‘SK’ in select bacteria and fungi. We have discovered a novel triple fusion protein of K, S, and pyrophosphatase (P) in several protozoan genomes within the Stramenopile lineage. These triple domain fusion proteins led us to hypothesize that pyrophosphatase enzymes and sulfate activation enzymes physically interact to impact the thermodynamics of the sulfate activation pathway. In support of this hypothesis, we demonstrate through biochemical assays that separately encoded KS and P proteins physically interact and that KS/P complexes activate more sulfate than KS alone. We also conclude on the basis of phylogenetic analyses that all known KS fusions originate from a single fusion event early in the eukaryotic lineage. Strikingly, our analyses support the same conclusion for all known SK fusions. These observations indicate that the patchwork of fused and nonfused S and K genes observed in modern-day eukaryotes and prokaryotes are the result of the two ancestral fusion genes evolving by an assortment of gene fissions, duplications, deletions, and horizontal transfers in different lineages. Our integrative use of genomics, phylogenetics, and biochemistry to characterize pyrophosphatase as a new member of the sulfate activation pathway should be effective at identifying new protein members and connections in other molecular pathways. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Nucleotide sequence data reported here are available in the GenBank/DDBJ/EMBL databases under accession number EU352210.