X-ray Crystal Structure and Specificity of the Plasmodium falciparum Malaria Aminopeptidase PfM18AAP

The malarial aminopeptidases have emerged as promising new drug targets for the development of novel antimalarial drugs. The M18AAP of Plasmodium falciparum malaria is a metallo-aminopeptidase that we show demonstrates a highly restricted specificity for peptides with an N-terminal Glu or Asp residue. Thus, the enzyme may function alongside other aminopeptidases in effecting the complete degradation or turnover of proteins, such as host hemoglobin, which provides a free amino acid pool for the growing parasite. Inhibition of PfM18AAP's function using antisense RNA is detrimental to the intra-erythrocytic malaria parasite and, hence, it has been proposed as a potential novel drug target. We report the X-ray crystal structure of the PfM18AAP aminopeptidase and reveal its complex dodecameric assembly arranged via dimer and trimer units that interact to form a large tetrahedron shape that completely encloses the 12 active sites within a central cavity. The four entry points to the catalytic lumen are each guarded by 12 large flexible loops that could control substrate entry into the catalytic sites. PfM18AAP thus resembles a proteasomal-like machine with multiple active sites able to degrade peptide substrates that enter the central lumen. The Plasmodium enzyme shows significant structural differences around the active site when compared to recently determined structures of its mammalian and human homologs, which provides a platform from which a rational approach to inhibitor design of new malaria-specific drugs can begin.     

Synthesis of a peptidocalix[4]arene library and identification of compounds with hydrolytic activity

A 120 member library of peptidocalix[4]arenes was synthesized and screened for catalysis of the hydrolysis of p-nitrophenyl acetate. His-Ser-His-calix[4]arene was found to catalyze this reaction with v(0)=3.24 x 10(-8)M/s, an increase of 1520% above background and 30% above the tripeptide (His-Ser-His) alone.     

Evidence for diet partitioning among three coexisting native freshwater fishes in South Africa's Cape Fold Ecoregion

The partitioning of limited resources commonly explains how different species can coexist within the same ecological community. In this 2010 study, the diets of three coexisting freshwater fishes (Cape galaxias Galaxias zebratus, n = 27; Cape kurper Sandelia capensis, n = 60; Breede River redfin Pseudobarbus burchelli, n = 77) were characterised and compared in three headwater streams in South Africa's Cape Fold Ecoregion using gut contents and stable isotope analyses. These data were analysed to ascertain whether the three species exploit distinct trophic niches. Both approaches provided evidence that these species occupy different trophic niches, though with some overlap. However, dietary differences among sites were not consistent and were probably influenced by site-specific factors like resource availability. Pseudobarbus burchelli had a broader niche breadth at Tierkloof Stream than the other two species, but not at Waaihoek or Tierstel Streams. Our results also suggest that P. burchelli consumed a more omnivorous diet than do the other two species, whereas S. capensis occupied a higher trophic position than the other two species and consumed vertebrates. Our findings suggest that these species occupy non-equivalent feeding niches in Cape Fold Ecoregion headwater streams, and that diet partitioning might facilitate their coexistence in these systems.     

The Biotransformation of Propylene to Propylene Oxide by Methylococcus capsulatus (Bath): 3. Reactivation of Inactivated Whole Cells to Give a High Productivity System

Methylococcus capsulatus (Bath) possesses methane monooxygenases (soluble - (sMMO) and particulate - (pMMO)) which are able to catalyse the epoxidation of propylene to propylene oxide. In a previous paper we have shown that the production of the epoxide caused a rapid inactivation of the bioconversion process (Stanley et al, 1992). This paper shows that cultures containing pMMO, inactivated by propylene oxide production, could be completely reactivated in the presence of growth substrates within 5 h after the removal of propylene oxide so long as the propylene oxide production rate was below 150 nmol min^-1 [mg dry weight cells]^-1. Reactivation under these conditions was detectable within 30 min of propylene oxide removal. On the other hand, cells inactivated by propylene oxide production rates in excess of 150 nmol min^-1 [mg dry weight]^-1 did not begin to recover activity within the 30 min period. Furthermore a lag period was observed before reactivation began which was dependent upon the initial production rate. Cultures possessing sMMO took twice as long to recover their activity compared with cells containing pMMO.

Reactivation of propylene oxide production could occur without growth, but the process required the presence of a carbon and energy source (methane or methanol), sulphur, nitrogen and oxygen, although copper (which is normally involved in pMMO activity) was not required. It was shown that de novo protein synthesis was required for reactivation of activity.

Production rates of 12 g 1^-1 d^-1 could be maintained for longer than three weeks in a single phase production process and rates up to 30 g 1^-1 d^-1 were achieved in a two stage process. Using Methylocystis parvus (OBBP) rates of up to 90 g 1^-1 d^-1 were attained over a one week period.     

Solubilisation of methane monooxygenase from Methylococcus capsulatus (Bath)

The membrane-bound (particulate) form of methane monooxygenase from Methylococcus capsulatus (Bath) has been solubilised using the non-ionic detergent dodecyl-beta-D-maltoside. A wide variety of detergents were tested and found to solubilise membrane proteins but did not yield methane monooxygenase in a form that could be subsequently activated. After solubilisation with dodecyl-beta-D-maltoside, enzyme activity was recovered using either egg or soya-bean lipids. Attempts to further purify the solubilized methane monooxygenaser protein into its component polypeptides were unsuccessful and resulted in complete loss of enzyme activity. The major polypeptides present in the solubilised enzyme had molecular masses of 49 kDa, 23 kDa and 22 kDa which were similar to those seen in crude extracts [Prior, S. D. & Dalton H. (1985) J. Gen. Microbiol. 131, 155-163]. Studies on substrate and inhibitor specificities indicated that the membrane-associated and solubilised forms of methane monooxygenase were quite similar to each other but differed substantially from the well-characterised soluble methane monooxygenase found in cells grown in a low copper regime and synthesised independently of the particulate methane monooxygenase.     

Interactions Between DDT and River Fungi: I. Effects of p,p′-DDT on the Growth of Aquatic Hyphomycetes

Concentrations of p,p'-DDT between 0.1 and 60 mug/ml enhanced the growth rate of Heliscus submersus, and concentrations greater than 2 mug/ml had a similar effect on Tetracladium setigerum, Varicosporium elodeae, and Clavariopsis aquatica. The rate of growth of each fungus increased with increased DDT concentration.     

Influence of various soil factors on the effects of ferulic acid on leaf expansion of cucumber seedlings

Summary Cucumber seedlings were grown in a Portsmouth soil-sand system to study how varying soil clay and organic matter content might modify cucumber seedling response to ferulic acid, a reported allelopathic agent. Leaf area expansion of cucumber seedlings, soil respiration, and soil solution concentrations of ferulic acid were monitored. Leaf area, mean absolute rates of leaf expansion, and shoot dry weight of cucumber seedlings were significantly reduced by ferulic acid concentrations ranging from 10 to 70 μg/g dry soil. Ferulic acid was applied every other day, since it rapidly disappeared from soil solution as a result of retention by soil particles, utilization by microbes and/or uptake by roots. The amount of ferulic acid retained (i.e., adsorbed, polymerized,etc.) by soil particles appeared to be secondary to microbial utilization and/or uptake by roots. Varying clay (5.3 to 9.8 g/cup) and organic matter (2.0 to 0.04g/cup) contents of the soil appeared to have little impact on the disappearance of ferulic acid from soil solution under “ideal” growth conditions for cucumber seedlings unless larger amounts of ferulic acid were added to the soil; in this case 200 μg/g. The addition of ferulic acid to the soil materials substantially increased the activity of the soil microbes. This latter conclusion is based on recovery of ferulic acid from soil solution and soil respiration measurements. Paper No. 10347 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, N C 27695-7601. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of the product named, nor criticism of similar ones not mentioned.     

The effect of cleft lip on adults' responses to faces: cross-species findings

Cleft lip and palate is the most common of the congenital conditions affecting the face and cranial bones and is associated with a raised risk of difficulties in infant-caregiver interaction; the reasons for such difficulties are not fully understood. Here, we report two experiments designed to explore how adults respond to infant faces with and without cleft lip, using behavioural measures of attractiveness appraisal ('liking') and willingness to work to view or remove the images ('wanting'). We found that infants with cleft lip were rated as less attractive and were viewed for shorter durations than healthy infants, an effect that was particularly apparent where the cleft lip was severe. Women rated the infant faces as more attractive than men did, but there were no differences in men and women's viewing times of these faces. In a second experiment, we found that the presence of a cleft lip in domestic animals affected adults' 'liking' and 'wanting' responses in a comparable way to that seen for human infants. Adults' responses were also remarkably similar for images of infants and animals with cleft lip, although no gender difference in attractiveness ratings or viewing times emerged for animals. We suggest that the presence of a cleft lip can substantially change the way in which adults respond to human and animal faces. Furthermore, women may respond in different ways to men when asked to appraise infant attractiveness, despite the fact that men and women 'want' to view images of infants for similar durations.     

应用气-质联用仪测定三种螺旋藻中的甾醇成分

应用GLC/MS联用仪对室内培养的钝顶螺旋藻(Spirulina platensis (Nordstedt) Geitler)、极大螺旋藻(S.maxima (Stechell & Gardiner) Geitler)和盐泽螺旋藻(S.subsalsa Oerst)的甾醇成分进行了测定。从钝顶螺旋藻和盐泽螺旋藻中共分出11个相同的甾醇组分:胆甾醇、胆甾烷醇、芸苔甾醇、麦角甾醇、海绵甾醇、菜子甾醇、豆甾醇、24-乙基-Δ~(5,7,22)-胆甾醇、β-谷甾醇、异岩藻甾醇和4α,23,24-三甲基Δ~(5,22)-胆甾醇;从极大螺旋藻中只分离出8个甾醇组分。其中胆甾醇含量最高。4α,23,24-三甲基-Δ~(5,22)-胆甾醇为蓝藻中首次报导。