Records of East African lichens in cool temperate Australia

Three East African lichens, Cladonia praetermissa var. modesta comb, nov., Phaeophyscia fumosa, Pyxine nubila are recorded from cool temperate Australia and their distribution and ecology are discussed. The disjunction in distribution is considered unlikely to be due to long-distance dispersal and the species may represent ancient relicts.     

Structure of Functional Staphylococcus aureus α-Hemolysin Channels in Tethered Bilayer Lipid Membranes

We demonstrate a method for simultaneous structure and function determination of integral membrane proteins. Electrical impedance spectroscopy shows that Staphylococcus aureus α-hemolysin channels in membranes tethered to gold have the same properties as those formed in free-standing bilayer lipid membranes. Neutron reflectometry provides high-resolution structural information on the interaction between the channel and the disordered membrane, validating predictions based on the channel's x-ray crystal structure. The robust nature of the membrane enabled the precise localization of the protein within 1.1 Å. The channel's extramembranous cap domain affects the lipid headgroup region and the alkyl chains in the outer membrane leaflet and significantly dehydrates the headgroups. The results suggest that this technique could be used to elucidate molecular details of the association of other proteins with membranes and may provide structural information on domain organization and stimuli-responsive reorganization for transmembrane proteins in membrane mimics.     

Genetic characterisation of seed yield and fertility traits in perennial ryegrass (<Emphasis Type="Italic">Lolium perenne</Emphasis> L.)

Seed yield is a trait of major interest for the key grassland species Lolium perenne L. An F2 mapping population of perennial ryegrass (VrnA), recently characterised for vernalisation response, was assessed in a glasshouse for traits related to seed yield based on a lattice design with four replications over 2 years. The traits heading date, plant height, length of panicles, number of panicles per plant, seed yield per panicle, flag leaf length, flag leaf width and seed yield per plant revealed repeatabilities ranging from 41 to 76% and a considerable amount of genetic variation in the VrnA population. Path analysis partitioned the direct and indirect effects of seed yield components on seed yield per plant. Seed yield per panicle showed the highest effect on total seed yield. The adjusted mean values of each trait and a genetic linkage map consisting of 97 anonymous and 85 gene associated DNA markers were used for quantitative trait loci (QTL) analysis. Of particular interest were two QTL on linkage group (LG) 1 and LG 2, explaining 41 and 18%, respectively, of the observed phenotypic variation for the trait seed yield per panicle. Both QTL co-located with two major QTL for total seed yield per plant possibly representing the S and Z loci of the gametophytic self incompatibility (SI) system of perennial ryegrass. The diversity of SI alleles in mapping parents and the degree of heterozygosity at SI loci in the full sib progeny determines the interference of self incompatibility with seed production.     

Bacillus subtilis polynucleotide phosphorylase 3′-to-5′ DNase activity is involved in DNA repair

In the presence of Mn²⁺, an activity in a preparation of purified Bacillus subtilis RecN degrades single-stranded (ss) DNA with a 3′ → 5′ polarity. This activity is not associated with RecN itself, because RecN purified from cells lacking polynucleotide phosphorylase (PNPase) does not show the exonuclease activity. We show here that, in the presence of Mn²⁺ and low-level inorganic phosphate (P_i), PNPase degrades ssDNA. The limited end-processing of DNA is regulated by ATP and is inactive in the presence of Mg²⁺ or high-level P_i. In contrast, the RNase activity of PNPase requires Mg²⁺ and P_i, suggesting that PNPase degradation of RNA and ssDNA occur by mutually exclusive mechanisms. A null pnpA mutation (ΔpnpA) is not epistatic with ΔrecA, but is epistatic with ΔrecN and Δku, which by themselves are non-epistatic. The addA5, ΔrecO, ΔrecQ (ΔrecJ), ΔrecU and ΔrecG mutations (representative of different epistatic groups), in the context of ΔpnpA, demonstrate gain- or loss-of-function by inactivation of repair-by-recombination, depending on acute or chronic exposure to the damaging agent and the nature of the DNA lesion. Our data suggest that PNPase is involved in various nucleic acid metabolic pathways, and its limited ssDNA exonuclease activity plays an important role in RecA-dependent and RecA-independent repair pathways.     

Immunogenic properties of amyloid beta oligomers

Background

The central molecule in the pathogenesis of Alzheimer’s disease (AD) is believed to be a small-sized polypeptide – beta amyloid (Aβ) which has an ability to assemble spontaneously into oligomers. Various studies concerning therapeutic and prophylactic approaches for AD are based on the immunotherapy using antibodies against Aβ. It has been suggested that either active immunization with Aβ or passive immunization with anti-Aβ antibodies might help to prevent or reduce the symptoms of the disease. However, knowledge on the mechanisms of Aβ-induced immune response is rather limited. Previous research on Aβ1-42 oligomers in rat brain cultures showed that the neurotoxicity of these oligomers considerably depends on their size. In the current study, we evaluated the dependence of immunogenicity of Aβ1-42 oligomers on the size of oligomeric particles and identified the immunodominant epitopes of the oligomers.

Results

Mice were immunized with various Aβ1-42 oligomers. The analysis of serum antibodies revealed that small Aβ1-42 oligomers (1–2 nm in size) are highly immunogenic. They induced predominantly IgG2b and IgG2a responses. In contrast, larger Aβ1-42 oligomers and monomers induced weaker IgG response in immunized mice. The monoclonal antibody against 1–2 nm Aβ1-42 oligomers was generated and used for antigenic characterization of Aβ1-42 oligomers. Epitope mapping of both monoclonal and polyclonal antibodies demonstrated that the main immunodominant region of the 1–2 nm Aβ1-42 oligomers is located at the amino-terminus (N-terminus) of the peptide, between amino acids 1 and 19.

Conclusions

Small Aβ1-42 oligomers of size 1–2 nm induce the strongest immune response in mice. The N-terminus of Aβ1-42 oligomers represents an immunodominant region which indicates its surface localization and accessibility to the B cells. The results of the current study may be important for further development of Aβ-based vaccination and immunotherapy strategies.