Structural analysis of the phytophagous insect guilds associated with the roots of Centaurea maculosa Lam. C. diffusa Lam., and C. vallesiaca Jordan in Europe:

Summary During extensive field surveys in central and eastern Europe, 21 herbivorous root insect species were found on Centaurea maculosa ssp. rhenana Boreau, 12 species on C. diffusa Lam. and 11 species on C. vallesiaca Jordan, representing 12 families in 4 orders. The large geographic distribution (species-area function), the high number of Centaurea spp. present (host speciation rate), and the high apparency of the rosettes and the rich food resources offered by the roots during winter, together with their poor accessibility, correlate with the high number of specialist feeders associated with the roots of C. maculosa and C. diffusa. The members of the taxonomically diverse root entomofauna exploit specific structures of the tap root (food niches). Interspecific competition among members of food niches, as well as species-specific responses to different phenological stages (for oviposition) and tissues (for larval development) are thought to be responsible for the high predictability in guild structure. The relatively low levels of host plant attack (two thirds of the roots were unattacked) and the fact that food niches remained unoccupied in most of the regions suggest, however, that the majority of the studied guilds do not represent equilibrium assemblages. Ecological (different habitats), climatic (transitional zone) and historical (ancient pre-Pleistocene communities) factors could account for the highest values of species diversity, infestation levels, species packing and food niche utilization, which are found on C. maculosa in E. Austria/NW. Hungary, compared to other regions. A positive correlation between species packing (number of root-feeding species per population) and infestation rates (percent of roots attacked) was only found for the more stable, semi-natural habitats. A comparative analysis of the regional root insect guilds of C. maculosa with corresponding data for the phytophagous insects associated with the flower heads revealed distinct taxonomical differences, but a high degree of numerical and structural similarity. The different geographical regions are similarly ranked for host plant attack, herbivore pressure, average species packing and level of food niche utilization.     

A null model of guild proportionality,applied to stratification of a New Zealand temperate rain forest

Summary Much ecological theory assumes that the number of species that can coexist (by species packing) is limited, because competitive exclusion occurs when any pair of species within a guild is too similar — species saturation or niche limitation. If such niche limitation occurs, the proportion of species in each guild should be relatively constant — guild proportionality. This concept is applied to the guilds represented by strata in a forest. A method is produced, and used to examine a New Zealand temperate rain forest. Most strata showed no deviation from a null model of no niche limitation, i.e. no tendency to guild proportionality. The proportion of lianes was more variable than in the null model, tending to be inversely related to the proportion of epiphytes, Canopy tree proportion was significantly more constant than in the null model, but this could be interpreted as a limit caused by the size of a canopy tree individual.     

Effects of flowering plant's patch size on species composition of pollinator communities,foraging strategies,and resource partitioning in bumblebees (Hymenoptera: Apidae)

Summary In 4 common Middle-European mainly bumblebee-pollinated plant species (Impatiens glandulifera, Echium vulgare, Aconitum napellus, Symphytum officinale) the influence of patch size on species composition of the pollinator community was studied. Short-tongued species were most dominant in large patches, while small patches were frequented by middle- and long-tongued bumblebees. This phenomenon was extremely obvious in Symphytum officinale and Aconitum napellus, where short-tongued species had bitten a hole in nearly every flower of large patches. Long-tongued species were forced to small patches, where nectarrobbing occurred only exceptionally. In small patches visitationrate (Number of visits per flower per hour) was not lower but either equal or even higher then in large patches. Nectar measurements in Echium vulgare showed, that not only the mean quantity of nectar but also the variance was lower in small patches. As a result, the possible gain can be predicted much more precisely in a small patch than in a large one, and bumblebees have less difficulties in making the right foraging decisions. According to this, foraging strategies depend on patch size. This was confirmed by a computer simulation. The conclusion can be drawn, that many bumblebee species are able to share the same resource by using different patch sizes. Since large flower patches occur mainly in man-made habitats, the dominance of short-tongued species in many bumblebee communities studied by other authors may be unnatural.Supported by the Landesgraduiertenförderung Baden-Württemberg     

Reevaluation of the amino acid sequence of porcine follitropin

We have reevaluated the sequence of porcine follicle-stimulating hormone (pFSH) with more recent protein-sequencing methodology. This has led to revision of the earlier proposed sequence. As with almost all reported gonadotropin -subunits, NH₂-terminal heterogeneity was found in the porcine FSH -subunit (FSH), starting with residue Phe (1), Asp (3), Gly (4), or Thr (7). In the -subunit, there were found to be at least two molecular species, starting with residue Asn (1) (minor 20%) or Cys (3) (major 80%) as NH₂-terminal and ending at residue Glu (108) as COOH-terminal. The net effect of the present revisions is to increase the homology of pFSH with other reported follitropin sequences. Apparent differences in the half-cystine placements in a previous proposal for pFSH compared with other species of FSH are no longer tenable. The half-cystine placements thus remain a constant structural feature throughout the gonadotropin hormones (choriogonadotropin, follitropin, and lutropin).     

Conformational change of bovine serum albumin by heat treatment

The thermal denaturation of bovine serum albumin (BSA) was studied at pH 2.8 and 7.0 in the range of 2–65°C. The relative proportions of -helix, -structure, and disordered structure in the protein conformation were determined as a function of temperature, by the curve-fitting method of circular dichroism spectra. With the rise of temperature at pH 7.0, the proportion of -helix decreased above 30°C and those of -structure and disordered structure increased in the same temperature range. The structural change was reversible in the temperature range below 45°C. However, the structural change was partially reversible upon cooling to room temperature subsequent to heating at 65°C. On the other hand, the structural change of BSA at pH 2.3 was completely reversible in the temperature range of 2–65°C, probably because the interactions between domains and between subdomains might disappear due to the acid expansion. The secondary structure of disulfide bridges-cleaved BSA remained unchanged during the heat treatment up to 65°C at pH 2.8 and 7.0.     

Structure of heavy and light chain subunits of type A botulinum neurotoxin analyzed by circular dichroism and fluorescence measurements

Summary The secondary and tertiary structural features of botulinum neurotoxin (NT) serotype A, a dichain protein (M_r 145 000), and its two subunits, the heavy (H) and light (L) chains (M_r 97 000 and 53 000, respectively) were examined using circular dichroism and fluorescence spectorscopy. Nearly 70% of the amino acid residues in each of the three polypeptide preparations were found in ordered structure (sum of helix, sheet and turns). Also, the helix, sheet, turns and random coil contents of the dichain NT were nearly equal to the weighted mean of each of these secondary structure parameters of the L and H chains; e.g., sum of helix of L chain (22%) and H chain (18.7%), as weighted mean, 19.8% was similar to that of NT (20%). These agreements suggested that the secondary structures of the subunits of the dichain NT do not significantly change when they are separated as isolated L and H chains. Fluorescence emission maximum of L chain, 4 nm less (blue shift) than that of H chain, suggested relatively more hydrophobic environment of fluorescent tryptophan residue(s) of L chain. Tryptophan fluorescence quantum yields of L chain, H chain and the NT, 0.072, 0.174 and 0.197, respectively, suggested that a) an alteration in the micro-environment of the tryptophan residues was possibly caused by interactions of L and H chain subunits of the NT and b) quantum yields for L and H chains were altered when they are together as subunits of the NT. Possible implications of structural features of the L and H chains, their interactions and the molecular mechanism of action of botulinum NT are assessed.     

Synthesis and conformational analysis of aib-containing peptide modelling for N-glycosylation site in N-glycoprotein

A tetrapetide containing an Aib residue, Boc-Asn-Aib-Thr-Aib-OMe, was synthesized as a peptide model for the N-glycosylation site in N-glycoproteins. Backbone conformation of the peptide and possible intramolecular interaction between the Asn and Thr side chains were elucidated by means of n.m.r. spectroscopy. Temperature dependence of NH proton chemical shift and NOE experiments showed that Boc-Asn-Aib-Thr-Aib-OMe has a tendency to form a β-turn structure with a hydrogen bond involving Thr and Aib⁴ NH groups. Incorporation of Aib residues in the peptide model promotes folding of the peptide backbone. With folded backbone conformation, carboxyamide protons of the Asn residue are not involved in hydrogen bond network, while the OH group of the Thr residue is a candidate for a hydrogen bond in DMSO-d₆ solution.     

DNA structures associated with autonomously replicating sequences from plants

DNA fragments capable of conferring autonomous replicating ability to plasmids inSaccharomyces cerevisiae were isolated from four different plant genomes and from the Ti plasmid ofAgrobacterium tumefaciens. The DNA structure of these autonomously replicating sequences (ARSs) as well as two from yeast were studied using retardation during polyacrylamide gel electrophoresis and computer analysis as measures of sequence-dependent DNA structures. Bent DNA was found to be associated with the ARS elements. An 11 bp ARS consensus sequence required for ARS function was also identified in the elements examined and was flanked by unusually straight structures which were rich in A+T content. These results show that the ARS elements from genomes of higher plants have structural and sequence features in common with ARS elements from yeast and higher animals.Supported by Grant 1RO1-GM41708-O1 from the National Institute of Health.     

Purification and immunological properties of an NAD(H) dependent glutamate dehydrogenase from soybean cells (Glycine max L.)

Studies were carried out on glutamate dehydrogenase (GDH, EC 1.4.1.2) isolated from the SB1 and SB3 soybean (Glyciene max L. cv. Mandarin) cell cultures. The NAD(H) dependent enzyme from SB1 and SB3 cells was purified to homogeneity, and that from the SB3 cells studied in detail. It was shown to be activated by calcium. The molecular weight of the native enzyme was found to be 263 000 ± 12 000. The molecular weight of the subunits was shown to be 41 000 ± 2000, which indicates that the enzyme has a hexameric structure. Anti-GDH antibodies were produced in rabbits, to GDH purified to homogeneity from both cell cultures. Each antibody preparation reacted with the purified enzyme produced from either cell culture. Antibodies to GDH from SB3 cells were utilized to study the apparent induction of GDH, which occurs when these cells are grown in a medium with ammonium ions as the sole nitrogen source. The increase in GDH activity was shown to be due to de-novo protein synthesis. The anti-SB3-GDH antibody preparation was also tested for cross reactivity with crude GDH preparations from a number of plant sources, and purified GDH from a number of other organisms. The antibody was shown to cross react with a number of the GDH preparations.