Rational behavioral response and the transmission of STDs

The susceptible-infected (SI) model is extended by allowing for individual optimal choices of self-protective actions against infection, where agents differ with respect to preferences and costs of self-protection. It is shown that a unique endemic equilibrium prevalence exists when the basic reproductive number of a STD is strictly greater than unity, and that the disease-free equilibrium is the unique steady state equilibrium when the basic reproductive number is less than or equal to one. Unlike in models that take individual behavior as given and fixed, the endemic equilibrium prevalence need not vary monotonically with respect to the basic reproductive number. Specifically, with endogenously determined self-protective behavior, a reduction in the basic reproductive number may in fact increase the endemic equilibrium prevalence. The global stability of the endemic steady state is established for the case of a homogeneous population by showing that, for any non-zero initial disease prevalence, there exists an equilibrium path which converges to the endemic steady state.     

Dufour gland of the digger wasp<Emphasis Type="Italic"> Liris niger:</Emphasis> structure and developmental and biochemical aspects

The tubiform Dufour gland in the digger wasp species Liris niger is about 1.0 mm long ( 0.15 mm). An alternating arrangement of longitudinal and circumferential bundles of striated muscle fibers surrounds the gland. The Dufour gland, together with the venom gland, enters the sting base and terminates in the sting. The glandular epithelium is monolayered. Glands about 3 day after imaginal ecdysis have an empty lumen but a thick lining epithelium. The gland cells are characterized by a well-developed vesicular smooth endoplasmic reticulum, sparse rough ER and numerous free ribosomes. They also exhibit several electron-lucent vesicles and autophagic vacuoles. Secretion of electron-dense material via the gland cuticle into the gland lumen is apparent. Glands more than 20 days after imaginal ecdysis display a large lumen and a thin epithelium. The cells show signs of degeneration with numerous cytolytic inclusions. Dufour gland liquid contains numerous polypeptides of molecular weights ranging from 14 to about 200 kDa. In addition the secretion consists predominantly of straight-chain hydrocarbons, accompanied by small amounts of esters. The major hydrocarbons are pentadecane and (Z)-8-heptadecene. Dufour gland secretion may have several functions: (1) the polypeptides might be involved in the gluing process of the eggs, while (2) the hydrocarbon oils may function as lubricants for the lancets and (3) might soften the secretion, thus allowing easier application of the glue. The lipophilic volatile material (4) might also be involved in pheromonal signaling.     

Down the Slippery Slope: Plastid Genome Evolution in Convolvulaceae

Cuscuta (dodder) is the only parasitic genus found in Convolvulaceae (morning-glory family). We used long PCR approach to obtain large portions of plastid genome sequence from Cuscuta sandwichiana in order to determine the size, structure, gene content, and synteny in the plastid genome of this Cuscuta species belonging to the poorly investigated holoparasitic subgenus Grammica. These new sequences are compared with the tobacco chloroplast genome, and, where data are available, with corresponding regions from taxa in the other Cuscuta subgenera. When all known plastid genome structural rearrangements in parasitic and nonparasitic Convolvulaceae are considered in a molecular phylogenetic framework, three categories of rearrangements in Cuscuta are revealed: plesiomorphic, autapomorphic, and synapomorphic. Many of the changes in Cuscuta, previously attributed to its parasitic mode of life, are better explained either as plesiomorphic conditions within the family, i.e., conditions shared with the rest of the Convolvulaceae, or, in most cases, autapomorphies of particular Cuscuta taxa, not shared with the rest of the species in the genus. The synapomorphic rearrangements are most likely to correlate with the parasitic lifestyle, because they represent changes found in Cuscuta exclusively. However, it appears that most of the affected regions, belonging to all of these three categories, have probably no function (e.g., introns) or are of unknown function (a number of open reading frames, the function of which, if any, has yet to be discovered).[Reviewing Editor: Dr. Debashish Bhattacharya]     

Atomic model of the E. coli membrane-bound protein translocation complex SecYEG

The Sec complex forms the core of a conserved machinery transporting proteins across or into membranes. In Escherichia coli SecYEG is active as an oligomer, but the structure predicts that the protein-conducting channel is formed by the monomer. A homology model of the E.coli complex was built using the atomic structure of Methanococcus jannaschii SecYEbeta. Another structure of the membrane-bound dimer was then determined by fitting the homology model to an 8A map of SecYEG determined by electron microscopy. We found that the substrate-binding site of the dimer has opened slightly and the plug domain moved toward the outside. This new position retains the channel in a closed state. These differences partially reflect the movements that have been proposed to occur during channel gating. Further opening of the substrate-binding pocket to bind and release bound substrate and displacement of the plug during secretion, presumably rely on the action of the partner proteins. The contacts arising at the dimer interface in the environment of the lipid bilayer may have activated the assembly.     

DNA-induced conformational changes in type II restriction endonucleases: the structure of unliganded HincII

The 2.1A crystal structure of the unliganded type II restriction endonuclease, HincII, is described. Although the asymmetric unit contains only a single monomer, crystal lattice contacts bring two monomers together to form a dimer very similar to that found in the DNA bound form. Comparison with the published DNA bound structure reveals that the DNA binding pocket is expanded in the unliganded structure. Comparison of the unliganded and DNA liganded structures reveals a simple rotation of subunits by 11 degrees each, or 22 degrees total, to a more closed structure around the bound DNA. Comparison of this conformational change to that observed in the other type II restriction endonucleases where DNA bound and unliganded forms have both been characterized, shows considerable variation in the types of conformational changes that can occur. The conformational changes in three can be described by a simple rotation of subunits, while in two others both rotation and translation of subunits relative to one another occurs. In addition, the endonucleases having subunits that undergo the greatest amount of rotation upon DNA binding are found to be those that distort the bound DNA the least, suggesting that DNA bending may be less facile in dimers possessing greater flexibility.     

The crystal structures of semi-synthetic aequorins

The photoprotein aequorin emits light by an intramolecular reaction in the presence of a trace amount of Ca(2+). Semi-synthetic aequorins, produced by replacing the coelenterazine moiety in aequorin with the analogues of coelenterazine, show widely different sensitivities to Ca(2+). To understand the structural basis of the Ca(2+)-sensitivity, we determined the crystal structures of four semi-synthetic aequorins (cp-, i-, br- and n-aequorins) at resolutions of 1.6-1.8 A. In general, the protein structures of these semi-synthetic aequorins are almost identical to native aequorin. Of the four EF-hand domains in the molecule, EF-hand II does not bind Ca(2+), and the loop of EF-hand IV is clearly deformed. It is most likely that the binding of Ca(2+) with EF-hands I and III triggers luminescence. Although little difference was found in the overall structures of aequorins investigated, some significant differences were found in the interactions between the substituents of coelenterazine moiety and the amino acid residues in the binding pocket. The coelenterazine moieties in i-, br-, and n-aequorins have bulky 2-substitutions, which can interfere with the conformational changes of protein structure that follow the binding of Ca(2+) to aequorin. In cp-aequorin, the cyclopentylmethyl group that substitutes for the original 8-benzyl group does not interact hydrophobically with the protein part, giving the coelenterazine moiety more conformational freedom to promote the light-emitting reaction. The differences of various semi-synthetic aequorins in Ca(2+)-sensitivity and reaction rate are explained by the capability of the involved groups and structures to undergo conformational changes in response to the Ca(2+)-binding.     

Phylogeographic inferences concerning evolution of Brazilian Passiflora actinia and P. elegans (Passifloraceae) based on ITS (nrDNA) variation

BACKGROUND AND AIMS: Passiflora actinia and P. elegans, two markedly parapatric species, have their southern and northern distribution limits, respectively, in the most southern part of the Brazilian Atlantic Rain Forest. Despite the fact that they are classified in different taxonomic series, previous phylogenetic studies of this genus revealed a high genetic similarity between them. The aim of the present work was to analyse in more detail their geographical range in this region of overlap, to investigate intraspecific genetic variability and phylogeographic structure, and to search for possible hybrids. METHODS: Eighty-two localities were searched for these species, and nuclear internal transcribed spacer (ITS) sequences were investigated for 32 individuals of P. actinia, 20 of P. elegans and one putative interspecific hybrid. Plastid trnL-trnF and psbA-trnH were examined for 12 plants of each species and the putative hybrid. KEY RESULTS: Both species showed a high level of intraspecific and intra-individual ITS variability. Network analysis revealed a north-south geographic gradient in their intra and interspecific relationships. Mismatch analyses suggested a recent population expansion of P. elegans. The plastid markers showed restricted variability but, together with the nuclear data, they contributed to the identification of an interspecific hybrid of intermediate morphology at the border of the distribution of these two species. Both genetic and morphological data indicate the absence of an extensive hybridization zone between these species. CONCLUSIONS: Gene flow between lineages is the possible cause for the presence of different ITS sequences within a given plant, the absence of homogenization being due to the high degree of vegetative reproduction in the two species. Differentiation of P. actinia into geographic groups and the origin of P. elegans may have been influenced by the Atlantic Forest migration towards southern Brazil. The genetic pattern of the interspecific hybrid indicates that plastid inheritance in these species is at least sometimes paternal.     

Lysosomal enlargement in digestive cells of mussels exposed to cadmium, benzo[a]pyrene and their combination

Digestive cell lysosomes in mussels are known to respond to individual organic chemicals and metals after experimental exposure under laboratory conditions but reports dealing with the response to mixtures of pollutants are scarce. The aim of the present investigation was to compare the lysosomal responses elicited by exposure to a model organic chemical compound (benzo(a)pyrene, B[a]P), a model toxic metal (Cd) and their combination (B[a]P+Cd) under controlled laboratory conditions. Dimethylsulfoxide (DMSO) was used as vehicle to dissolve organic chemicals into seawater. Control mussels were either kept untreated in clean seawater or treated with DMSO. Digestive glands were excised on Day 21. beta-Glucuronidase activity was demonstrated in 8 mum cryotome sections. Lysosomal volume, surface and numerical densities (Vv, Sv and Nv), and surface-to-volume ratio (S/V) were quantified by image analysis. Lysosomal enlargement was evident in digestive cells of mussels exposed to either Cd, B[a]P or B[a]P+Cd. Such enlargement was more marked after exposure to B[a]P+Cd than to B[a]P, but did not reach the levels recorded after Cd exposure. It seems therefore that the presence of B[a]P reduced to some extent the effects of Cd on digestive cell lysosomes in mussels.     

The negative ecological impacts of a globally introduced species decrease with time since introduction

While there is a long‐history of biological invasions and their ecological impacts have been widely demonstrated across taxa and ecosystems, our knowledge on the temporal dynamic of these impacts remains extremely limited. Using a meta‐analytic approach, we investigated how the ecological impacts of non‐native brown trout (Salmo trutta), a model species with a 170‐year‐long and well‐documented history of intentional introductions across the globe, vary with time since introduction. We first observed significant negative ecological impacts immediately after the species introduction. Second, we found that the negative ecological impacts decrease with time since introduction and that the average ecological impacts become nonsignificant more than one century after introduction. This pattern was consistent across other ecological contexts (i.e., geographical location, levels of biological organization, and methodological approach). However, overall negative ecological impacts were more pronounced at the individual and population levels and in experimental studies. While the mechanisms leading to this decrease remain to be determined, our results indicate that rapid response of native organisms (e.g. adaptation, but also local extinction) may play an important role in this dynamic. Changes in native species traits and local extinction can have important conservation implications. Therefore, we argue that the decline of the negative ecological impacts over time should not be used as an argument to neglect the negative impacts of biological invasions.     

Interdomain Stabilization Impairs CD4 Binding and Improves Immunogenicity of the HIV-1 Envelope Trimer

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