Mechanism of protein folding. IV. Forming and breaking of disulfide bonds in bovine pancreatic tripsin inhibitor.

The folding mechanism of bovine pancreatic tripsin inhibitor (BPTI) is explained theoretically on the basis of the island model, where the driving force of folding is hydrophobic interaction. For this purpose, we take a look at the formation and breaking of disulfide bonds during the folding process of BPTI. The intermediate conformations and the native one are successfully obtained, which satisfy the so-called "lampshade" geometrical criterion for the formation of the disulfide bonds. The folding pathway is consistent with the renaturation experiment by Creighton. In addition, an elaborate treatment of side chains of amino acid residues by the software programme CHARMm confirms quantitatively the formation of disulfide bridges.     

Life-history and feeding habit ofTyphlodromus bambusae,a specific predator ofSchizotetranychus celarius (Acari: Phytoseiidae: Tetranychidae)

Studies on the life history and food habit ofTyphlodromus bambusae Ehara were carried out under aboratory conditions of 25±1°C, 60–80%rh and 159l:d.The egg-to-egg period of the predator which fed on eggs of the long-seta form ofSchizotetranychus celarius (Banks) was longer than those of the three phytoseiid species,Amblyseius eharai Amitai et Swirski,A. longispinosus (Evans) andA. paraki Ehara, which fed onTetranychus urticae Koch. The sex-ratio ofT. bambusae was not significantly different from those of the other three species. The long ovipositional period and the rather constant, low, reproductive rate observed inT. bambusae were remarkable.The intrinsic rate of natural increase (r _m) ofT. bambusae was 0.164 per day and it was very similar to ther _m of its prey,S. celarius. This observation supports the idea that there is a coincidence between the life-histories of spider-mite prey and their specific phytoseiid predators.Although females ofT. bambusae could feed on eggs ofAponychus corpuzae Rimando orSchizotetranychus recki Ehara which cohabit withS. celarius onSasa bamboo, their oviposition rate was lower than that onS. celarius eggs.Schizotetranychus celarius is thought to be a profitable prey species forT. bambusae, whileS. recki andA. corpuzae are only subsidiary, or alternative, prey.     

Conformation and dynamics of the [3-(13)C]Ala, [1-(13)C]Val-labeled truncated pharaonis transducer, pHtrII(1-159), as revealed by site-directed (13)C solid-state NMR: changes due to association with phoborhodopsin (sensory rhodopsin II)

We have recorded (13)C NMR spectra of the [3-(13)C]Ala, [1-(13)C]Val-labeled pharaonis transducer pHtrII(1-159) in the presence and absence of phoborhodopsin (ppR or sensory rhodopsin II) in egg phosphatidylcholine or dimyristoylphosphatidylcholine bilayers by means of site-directed (amino acid specific) solid-state NMR. Two kinds of (13)C NMR signals of [3-(13)C]Ala-pHtrII complexed with ppR were clearly seen with dipolar decoupled magic angle spinning (DD-MAS) NMR. One of these resonances was at the peak position of the low-field alpha-helical peaks (alpha(II)-helix) and is identified with cytoplasmic alpha-helices protruding from the bilayers; the other was the high-field alpha-helical peak (alpha(I)-helix) and is identified with the transmembrane alpha-helices. The first peaks, however, were almost completely suppressed by cross-polarization magic angle spinning (CP-MAS) regardless of the presence or absence of ppR or by DD-MAS NMR in the absence of ppR. This is caused by an increased fluctuation frequency of the cytoplasmic alpha-helix from 10(5) Hz in the uncomplexed states to >10(6) Hz in the complexed states, leading to the appearance of peaks that were suppressed because of the interference of the fluctuation frequency with the frequency of proton decoupling (10(5) Hz), as viewed from the (13)C NMR spectra of [3-(13)C]Ala-labeled pHtrII. Consistent with this view, the (13)C DD-MAS NMR signals of the cytoplasmic alpha-helices of the complexed [3-(13)C]Ala-pHtrII in the dimyristoylphosphatidylcholine (DMPC) bilayer were partially suppressed at 0 degrees C due to a decreased fluctuation frequency at the low temperature. In contrast, examination of the (13)C CP-MAS spectra of [1-(13)C]Val-labeled complexed pHtrII showed that the (13)C NMR signals of the transmembrane alpha-helix were substantially suppressed. These spectral changes are again interpreted in terms of the increased fluctuation frequency of the transmembrane alpha-helices from 10(3) Hz of the uncomplexed states to 10(4) Hz of the complexed states. These findings substantiate the view that the transducers alone are in an aggregated or clustered state but the ppR-pHtrII complex is not aggregated. We show that (13)C NMR is a very useful tool for achieving a better understanding of membrane proteins which will serve to clarify the molecular mechanism of signal transduction in this system.     

The dynamical consequences of developmental variability and demographic stochasticity for host-parasitoid interactions

Few age-structured models of species dynamics incorporate variability and uncertainty in population processes. Motivated by laboratory data for an insect and its parasitoid, we investigate whether such assumptions are appropriate when considering the population dynamics of a single species and its interaction with a natural enemy. Specifically, we examine the effects of developmental variability and demographic stochasticity on different types of cyclic dynamics predicted by traditional models. We show that predictions based on the deterministic fixed-development approach are differentially sensitive to variability and noise in key life stages. In particular, we find that the demonstration of half-generation cycles in the single-species model and the multigeneration cycles in the host-parasitoid model are sensitive to the introduction of developmental variability and noise, whereas generation cycles are robust to the intrinsic variability and uncertainty that may be found in nature.     

Biodiversity in different successional stages of Mediterranean enclaves distributed along Sinop Peninsula (Turkey)

The aim of this research was to evaluate plant diversity and the relationships between the distribution of Raunkiaer life forms and community structure, and species richness, at different successional stages in communities of Quercus ilex L., Erica arborea L. and Sarcopoterium spinosum (L.) Spach., distributed as enclaves in Sinop Province. Permanent sample plots were selected to determine plant diversity. The cover percentage of each plant species was recorded monthly during two vegetation periods. Raunkiaer life forms, and the Shannon–Wiener, Evenness, Simpson and Margalef indexes were determined. Twenty-three species in Quercus ilex, 96 species in Erica arborea, and 148 species in Sarcopoterium spinosum were identified. Hemicryptophyte dominancy was observed followed by phanerophytes in the Q. ilex community, and therophyte and hemicryptophyte dominancy in the E. arborea and S. spinosum communities, respectively. It was determined that the S. spinosum community was the most heterogeneous community while the Q. ilex community was more uniform than other communities. The variation in diversity indexes, homogeneity, and composition of life forms among communities adopting a similar climatic environment could result from a differentiation of environmental factors, which impact on community structuring, from biotic to abiotic at different successional stages of Mediterranean communities.     

A koinobiont parasitoid mediates competition and generates additive mortality in healthy host populations

Insects are subject to attack from a range of natural enemies. Many natural enemies, such as parasitoids, do not immediately, or ever, kill their victims but they are nevertheless important in structuring biological communities. The lag that often occurs between attack and host death results in mixed populations of healthy and parasitised hosts. However, little is understood about how the effects of parasitism during this lag period affect the competitive ability of parasitised hosts and how this, in turn, affects the survival and dynamics of the surviving healthy host populations. Here we investigate the impact of the timing of introduction, and the strength of that introduction, of a parasitoid natural enemy Venturia canescens (Gravenhorst) on the outcome of intraspecific competition between larvae of the Indian meal moth, Plodia interpunctella (Hübner). In contrast to healthy hosts alone, we find reduced survival of healthy larvae with increasing periods of exposure to greater numbers of parasitised conspecifics. This represents indirect mortality of the host, which is in addition to that imposed by parasitism itself. Furthermore, longer periods of exposure to parasitised larvae resulted in an increase in development time of healthy individuals and they were larger when they emerged as adults. These results are relevant to both insect–parasitoid and insect–pathogen systems where there is a lag in host death following infection or attack.     

Review: the potential impact of surface crystalline states of titanium for biomedical applications

In many biomedical applications, titanium forms an interface with tissues, which is crucial to ensure its long-term stability and safety. In order to exert control over this process, titanium implants have been treated with various methods that induce physicochemical changes at nano and microscales. In the past 20?years, most of the studies have been conducted to see the effect of topographical and physicochemical changes of titanium surface after surface treatments on cells behavior and bacteria adhesion. In this review, we will first briefly present some of these surface treatments either chemical or physical and we explain the biological responses to titanium with a specific focus on adverse immune reactions. More recently, a new trend has emerged in titanium surface science with a focus on the crystalline phase of titanium dioxide and the associated biological responses. In these recent studies, rutile and anatase are the major two polymorphs used for biomedical applications. In the second part of this review, we consider this emerging topic of the control of the crystalline phase of titanium and discuss its potential biological impacts. More in-depth analysis of treatment-related surface crystalline changes can significantly improve the control over titanium/host tissue interface and can result in considerable decreases in implant-related complications, which is currently a big burden on the healthcare system.