M42 aminopeptidase catalytic site: the structural and functional role of a strictly conserved aspartate residue

The M42 aminopeptidases are a family of dinuclear aminopeptidases widely distributed in Prokaryotes. They are potentially associated to the proteasome, achieving complete peptide destruction. Their most peculiar characteristic is their quaternary structure, a tetrahedron-shaped particle made of twelve subunits. The catalytic site of M42 aminopeptidases is defined by seven conserved residues. Five of them are involved in metal ion binding which is important to maintain both the activity and the oligomeric state. The sixth conserved residue, a glutamate, is the catalytic base deprotonating the water molecule during peptide bond hydrolysis. The seventh residue is an aspartate whose function remains poorly understood. This aspartate residue, however, must have a critical role as it is strictly conserved in all MH clan enzymes. It forms some kind of catalytic triad with the histidine residue and the metal ion of the M2 binding site. We assess its role in TmPep1050, an M42 aminopeptidase of Thermotoga maritima, through a mutational approach. Asp-62 was substituted with alanine, asparagine, or glutamate residue. The Asp-62 substitutions completely abolished TmPep1050 activity and impeded dodecamer formation. They also interfered with metal ion binding as only one cobalt ion is bound per subunit instead of two. The structure of Asp62Ala variant was solved at 1.5 Å showing how the substitution has an impact on the active site fold. We propose a structural role for Asp-62, helping to stabilize a crucial loop in the active site and to position correctly the catalytic base and a metal ion ligand of the M1 site.     

Influence of non‐crop plants on stink bug (Hemiptera: Pentatomidae) and natural enemy abundance in tomatoes

We investigated the effects of weed hosts on stink bug density and damage (Euschistus conspersus Uhler and Thyanta pallidovirens Stal), and a nectar bearing plant on natural enemies of stink bugs in the Sacramento Valley of California. Stink bug density and fruit damage were evaluated in processing tomatoes adjacent to weedy and cultivated borders. The density of E. conspersus was significantly greater in tomatoes adjacent to weedy borders in July but not during August/September. Thyanta pallidovirens was less abundant overall (19%), but was found in significantly greater densities adjacent to cultivated borders in July but not in August/September. Mean percent fruit damage by stink bugs was greater adjacent to the weedy border than the cultivated border, but this difference was not significant. Stink bug egg parasitism and generalist predator density were evaluated in fresh market tomatoes adjacent to a sweet alyssum (Lobularia maritima L.) border and an unplanted control border at three sites. Egg parasitism was significantly greater in the alyssum treatment for the 9–12 September sampling period. Jalysus wickhami VanDuzee (Hemiptera: Berytidae) density was significantly greater in the alyssum treatment in mid‐June. No other significant differences in predator populations were detected. Results of these two studies show that habitat manipulations have the potential to reduce densities of E. conspersus in tomato, the first step in developing a farmscape management plan for stink bug control.     

Characteristics of chimeric enzymes constructed between Thermotoga maritima and Agrobacterium tumefaciens β-glucosidases: Role of C-terminal domain in catalytic activity

The importance of C-terminal domain of β-glucosidase (family 3 glycosidase) from Thermotoga maritima, a hyper-thermophilic bacterium was investigated by gene shuffling. The amino acid sequences of β-glucosidases from T. maritima and A. tumefaciens share high degree of homology (approximately 40%). However, despite such a high homology, both enzymes exhibited quite distinct characteristics in terms of their pH and temperature profile and substrate specificities. To investigate the functional role of the C-terminal domains of T. maritima and A. tumefaciens β-glucosidases, three chimeric genes were constructed by shuffling at three selected regions. Out of the three chimeric enzymes, only two (Tm533/626At and Tm630/727At) were catalytically active. Parental and the chimeric enzymes were subsequently characterized for the substrate specificities and their response towards pH and temperature. Our results revealed that C-terminal domain was catalytically important. The study clearly establishes the significance of gene shuffling in probing the structure and function relationship in hyper-thermophilic bacterium and evolving enzymes with altered features.     

Do flowers wave to attract pollinators? A case study with Silene maritima

To answer the question whether flowers wave to attract pollinators, we determine: (1) the heritability of floral mobility; (2) whether wavy flowers attract more insects; (3) does the duration of pollination affect seed set; and (4) the relationship between seed set and floral mobility. The pollination ecology of Silene maritima was investigated. Flowers on stalks of different waviness were used to investigate the effect of floral movement on pollinator visits. There is heritable variation in both direct and indirect estimates of floral mobility. The highest insect total visitation times were associated with medium length thin stalks that were visited more frequently and by more insect species. Although mean individual visit durations were less than those of less mobile flowers, this was compensated for by increased visits. Observations of controlled pollinations show that when the visit times are low, so is seed set and therefore low and high mobility flowers might suffer from reduced fitness. Combining these observations provides a mechanism that could be driving stabilizing selection for flower stalk traits, with a trade-off applying between waving to attract pollinators and not being too mobile as to prevent effective pollination. Further evidence for stabilizing selection is provided by the relationship observed in the field between seed set and floral mobility where the highest levels of fitness was associated with intermediate levels of floral waving.     

海石竹的离体快繁及核型分析

以海石竹 (Armeriamaritima)的叶片为外植体 ,经离体培养诱导产生愈伤组织 ,再分化形成不定芽 ,并经过继代增殖和壮苗生根 ,获得完整的再生植株 ,最后对其再生植株进行核型分析。结果表明 ,海石竹叶片的愈伤组织诱导和分化的适宜培养基为MS +BA 1 .0mg/L +NAA 0 .2mg/L ,诱导初期进行 7d暗培养 ,最佳增殖培养基为MS+BA 1 .0mg/L +NAA 0 .1mg/L ,生根培养基为MS+NAA 0 .2mg/L。以上培养基均含蔗糖3 0 g/L ,琼脂 5g/L ,pH 5 .8。海石竹的核型公式为 2n=2x=1 8=1 0m +8sm ,存在染色体数目变异的现象。     

A novel bifunctional aspartate kinase-homoserine dehydrogenase from the hyperthermophilic bacterium,Thermotoga maritima

ABSTRACT

The orientation of the three domains in the bifunctional aspartate kinase-homoserine dehydrogenase (AK-HseDH) homologue found in Thermotoga maritima totally differs from those observed in previously known AK-HseDHs; the domains line up in the order HseDH, AK, and regulatory domain. In the present study, the enzyme produced in Escherichia coli was characterized. The enzyme exhibited substantial activities of both AK and HseDH. L-Threonine inhibits AK activity in a cooperative manner, similar to that of Arabidopsis thaliana AK-HseDH. However, the concentration required to inhibit the activity was much lower (K_0.5 = 37 μM) than that needed to inhibit the A. thaliana enzyme (K_0.5 = 500 μM). In contrast to A. thaliana AK-HseDH, Hse oxidation of the T. maritima enzyme was almost impervious to inhibition by L-threonine. Amino acid sequence comparison indicates that the distinctive sequence of the regulatory domain in T. maritima AK-HseDH is likely responsible for the unique sensitivity to L-threonine.

Abbreviations: AK: aspartate kinase; HseDH: homoserine dehydrogenase; AK–HseDH: bifunctional aspartate kinase–homoserine dehydrogenase; AsaDH: aspartate–β–semialdehyde dehydrogenase; ACT: aspartate kinases (A), chorismate mutases (C), and prephenate dehydrogenases (TyrA, T).     

Artificial diet for continuous maintenance of the maritima earwig Anisolabis maritima (Bonelli) (Dermaptera: Carcinophoridae)

Anisolabis maritima is an important predator for the eggs of the red palm weevil Rhynchophorous ferrugineus. It could be successfully reared in the laboratory, on an artificial diet composed of dry kidney beans, Brewers yeast, chicken, egg yolk, agar, ascorbic acid, mould inhibitors, vitamin B₁₂, folic acid and riboflavin.     

Ultra morphology of sensilla on the head and mouth parts of the earwig Anisolabis martima (Bonelli) (Dermaptera: Carcinophoridae)

The earwig Anisolabis maritima is a cosmopolitan insect with a worldwide distribution, omnivorous in feeding, eating the eggs of different insects. Recently recorded in Saudi Arabia as a beneficial predator on eggs and newly hatched larvae of the red palm weevil Rhyncophrous ferrugineus, scanning electron microscopy (SEM) observations revealed the presence of different kinds of receptor sensillae occurring on the head and mouth parts of A. maritime. The sensillae are the same, but differ in numbers on both sexes. The head surface bears three subtypes of trichoid sensillae, one type of ceoloconica. Labrum, labium, labial palps and maxillary palps, possess different kinds of sensillae. Three subtypes of trichoid have been identified on the labrum. The labium contained one type of tricoid and basiconic sensillae. There are great numbers and numerous sensillae cheatica differing in length distributed on the maxillary and the labial palps on all segments between other stutter spines. The last terminal segment of maxillary or labial palps bears the greatest number of the sensillae cheatica. Adult A. maritima may be introduced in the future as a beneficial predator of eggs of R. ferrugineus as a tool for integrated pest management.     

OBSERVATIONS ON THE COEXISTENCE OF FRESH AND SALTWATER INVERTEBRATES IN AN INLAND SALTWORKS

SUMMARY

The fauna of three excavated trenches in the floor of the dry salt-pan in the Brandfort district of the Orange Free State was investigated. Two were found to contain typical saline water invertebrate fauna such as Artemia sp. and the saltwater rotifer Brachionus plicatilis and were without vegetation, while the third supported dense stands of Ruppia maritima, the salt water rotifer Brachionus plicatilis and a variety of freshwater macro-invertebrates. We concluded that certain freshwater macro-invertebrates are able to tolerate saline water, and that this would give them a competitive advantage over stenohaline invertebrates in semi-arid and arid areas where a range of salinities occur within and among the endorheic pans in the region.