1H NMR study of the effect of variable ligand on heme oxygenase electronic and molecular structure

Heme oxygenase carries out stereospecific catabolism of protohemin to yield iron, CO and biliverdin. Instability of the physiological oxy complex has necessitated the use of model ligands, of which cyanide and azide are amenable to solution NMR characterization. Since cyanide and azide are contrasting models for bound oxygen, it is of interest to characterize differences in their molecular and/or electronic structures. We report on detailed 2D NMR comparison of the azide and cyanide substrate complexes of heme oxygenase from Neisseria meningitidis, which reveals significant and widespread differences in chemical shifts between the two complexes. To differentiate molecular from electronic structural changes between the two complexes, the anisotropy and orientation of the paramagnetic susceptibility tensor were determined for the azide complex for comparison with those for the cyanide complex. Comparison of the predicted and observed dipolar shifts reveals that shift differences are strongly dominated by differences in electronic structure and do not provide any evidence for detectable differences in molecular structure or hydrogen bonding except in the immediate vicinity of the distal ligand. The readily cleaved C-terminus interacts with the active site and saturation-transfer allows difficult heme assignments in the high-spin aquo complex.     

Copper(II) complexes with peptide fragments encompassing the sequence 122-130 of human doppel protein

Copper(II) complexes of the peptide fragment (Dpl122-130) encompassing the sequence 122-130 of human doppel protein were characterized by potentiometric, UV-Visible, CD and EPR spectroscopic methods. An analogous peptide, in which the aspartate residue was substituted by an asparagine amino acid, was synthesized in order to provide evidence on the possible role of carboxylate group in copper(II) coordination. It was found that the carboxylic group is directly involved in copper(II) coordination at acidic pH, forming the CuLH₂ species with Dpl122-130. This copper(II) complex displayed EPR parameters very similar to those of the analogous complex with the whole doppel protein. At pH higher than 7, the complexes showed magnetic parameters similar to those of the major species of protein formed in the pH range 7-8, with the metal coordination environment consisting of one imidazole and three amide nitrogen atoms. The comparison of Cu-Dpl122-130 binding constant values with those of the prion peptide fragments (PrP106-114), showed that doppel peptide had a higher metal binding affinity at acidic pH whereas the prion peptide fragment binds the metal tightly at physiological pH.     

p53 ubiquitination by Mdm2: A never ending tail?

p53 function is of critical importance in suppressing human cancer formation, highlighted by the fact that the majority of human tumors harbor compromised p53 activity. In normal cells, p53 is held at low levels in a latent form and cellular stress results in the rapid stabilization of p53. Mdm2 mediates ubiquitin-dependent degradation of p53 which plays a key role in maintaining cellular p53 levels. Ubiquitination was, until recently, considered a straightforward system involved in p53 degradation, but recent work has demonstrated how ubiquitination can alter p53 activity, not stability. In this review we summarize current understanding on p53 ubiquitination by Mdm2 with a particular focus on how the balance between protein levels and other post-translational modifications will direct the p53 response.     

Effects of flowering groundcover vegetation on diversity and activity of wasps in a farm shelterbelt in temperate Australia

Significant worldwide interest in conservation biological control in agricultural systems currently exists but little information is available on the usefulness of this approach in farm forestry. In a field experiment conducted in a native vegetated shelterbelt in central-west New South Wales, we measured the diversity of wasps in plots comprising Eucalyptus blakelyi Maiden (Myrtaceae) trees with and without a groundcover of Lobularia maritima (L.) Desv. (Brassicaceae). Vacuum samples revealed a greater abundance and species richness of parasitic wasps in the plots comprising trees surrounded by the L. maritima groundcover. Cotesia sp. (Hymenoptera: Braconidae), Pteromalus sp. (Hymenoptera: Pteromalidae), Anagyrus sp. (Hymenoptera: Encyrtidae), Entedoninae sp. and Eulophidae sp. 1 (Hymenoptera: Eulophidae) were the most common taxa. These were more abundant also in the trees with the L. maritima groundcover. Ardozyga stratifera (Meyrick) (Lepidoptera: Gelechiidae) larvae, that were naturally infesting the E. blakelyi trees, were significantly more parasitized in the trees with the L. maritima groundcover. Results indicate that parasitic wasps associated with a native-tree shelterbelt in Australia were amenable to manipulation via groundcover vegetation.

Phenotypic population divergence in terrestrial vertebrates at macro scales

Phenotypic divergence between populations, i.e. how much phenotypes within a species vary geographically, is critical to many aspects of ecology and evolution, including eco-geographical trends, speciation and coexistence. Yet, the variation of divergence across species with different ecologies and distributions and the relative role of adaptive causes remains little understood. We predict that genetic control vs. phenotypic plasticity of traits, geographical distance and (assuming adaptation) environmental differences should explain much of the phenotypic variability between populations. We tested these predictions with body sizes of 1447 populations in 98 terrestrial vertebrate species. Population phenotypic variability differs strongly across species, and divergence increases with increasing levels of clade-typical phenotypic plasticity, the area covered by populations and body size. Geographical distance and environmental dissimilarity are similarly important predictors of divergence within species, highlighting a potential role for biotic and environmental conditions. Increased availability of phylogeographical and ecological data should facilitate further understanding of population divergence drivers at broad scales.