A new rubisco-like protein coexists with a photosynthetic rubisco in the planktonic cyanobacteria Microcystis

Two genes encoding proteins related to large subunits of Rubisco were identified in the genome of the planktonic cyanobacterium Microcystis aeruginosa PCC 7806 that forms water blooms worldwide. The rbcL(I) gene belongs to the form I subfamily typically encountered in cyanobacteria, green algae, and land plants. The second and newly discovered gene is of the form IV subfamily and widespread in the Microcystis genus. In M. aeruginosa PCC 7806 cells, the expression of both rbcL(I) and rbcL(IV) is sulfur-dependent. The purified recombinant RbcL(IV) overexpressed in Escherichia coli cells did not display CO(2) fixation activity but catalyzed enolization of 2,3-diketo-5-methylthiopentyl-1-phosphate, and the rbcL(IV) gene rescued a Bacillus subtilis MtnW-deficient mutant. Therefore, the Microcystis RbcL(IV) protein functions both in vitro and in vivo and might be involved in a methionine salvage pathway. Despite variations in the amino acid sequences, RbcL(IV) shares structural similarities with all members of the Rubisco superfamily. Invariant amino acids within the catalytic site may thus represent the minimal set for enolization, whereas variations, especially located in loop 6, may account for the limitation of the catalytic reaction to enolization. Even at low protein concentrations in vitro, the recombinant RbcL(IV) assembles spontaneously into dimers, the minimal unit required for Rubisco forms I-III activity. The discovery of the coexistence of RbcL(I) and RbcL(IV) in cyanobacteria, the ancestors of chloroplasts, enlightens episodes of the chaotic evolutionary history of the Rubiscos, a protein family of major importance for life on Earth.     

Natural biocombinatorics in the polyketide synthase genes of the actinobacterium Streptomyces avermitilis

Modular polyketide synthases (PKSs) of bacteria provide an enormous reservoir of natural chemical diversity. Studying natural biocombinatorics may aid in the development of concepts for experimental design of genes for the biosynthesis of new bioactive compounds. Here we address the question of how the modularity of biosynthetic enzymes and the prevalence of multiple gene clusters in Streptomyces drive the evolution of metabolic diversity. The phylogeny of ketosynthase (KS) domains of Streptomyces PKSs revealed that the majority of modules involved in the biosynthesis of a single compound evolved by duplication of a single ancestor module. Using Streptomyces avermitilis as a model organism, we have reconstructed the evolutionary relationships of different domain types. This analysis suggests that 65% of the modules were altered by recombinational replacements that occurred within and between biosynthetic gene clusters. The natural reprogramming of the biosynthetic pathways was unambiguously confined to domains that account for the structural diversity of the polyketide products and never observed for the KS domains. We provide examples for natural acyltransferase (AT), ketoreductase (KR), and dehydratase (DH)–KR domain replacements. Potential sites of homologous recombination could be identified in interdomain regions and within domains. Our results indicate that homologous recombination facilitated by the modularity of PKS architecture is the most important mechanism underlying polyketide diversity in bacteria.     

Dyes from a twenty-first century perspective

In June 2008, the Biological Stain Commission sponsored A Seminar on Dyes and Staining the purpose of which was twofold: first, to show that very useful information applicable to biomedical dyes and staining is available from unrelated disciplines and second, to summarize modern thinking on how dyes, solvents, and tissues interact to produce selective staining. In this introduction to the papers from the symposium, we acknowledge that biomedical dye research has declined as newer technologies have gained importance. We should point out, however, that dyes and staining still are vitally important. Moreover, needs abound for innovative studies concerned with dye analysis, synthesis, and mode of action. Concepts and tools from unrelated fields hold promise for significant breakthroughs in many areas of interest.     

Body positions and movement patterns in female patients with congenital adrenal hyperplasia

Female patients with congenital adrenal hyperplasia (CAH; N = 33; 11-41 years), simple-virilizing (SV) patients (N = 19), salt-wasting (SW) patients (N = 13), and sister controls (N = 14) were compared with regard to their body positions and movement patterns. Data collection comprised both self assessments and mothers' assessments using 20 sex-dimorphic items with corresponding "more masculine" and "more feminine" versions for each variable, represented in photographs (forced-choice approach). Primarily based on mothers' assessments, single-item results suggested slightly more masculine positions and patterns for female CAH patients compared to sisters, for SW patients more distinct than for SV patients. Results from an 11-item scale ("motor behavior", alpha = 0.59) revealed differences between SW (more masculine) and SV patients for self assessments (P, one-tailed, < 0.09); sisters were in an intermediate position closer to the SV patients. According to mothers' assessments, the CAH patient group as a whole differed (more masculine) from sisters (P < 0.06); this finding was mainly accounted for by the SW group (P < 0.04). Complex analyses on the relationship of motor behavior and intervening variables (e.g., postnatal androgenization, onset of puberty, menarche, height, weight, sexual orientation) revealed very few significant results. Findings rather suggested organizational hormonal effects on body positions and movements prenatally; they are in line with main results from the interview section of the Hamburg CAH study (e.g., "Gender-related behavior"). An approach of this kind seems to be justified for investigating motor behavior in future psychoendocrine studies.     

Non-canonical localization of RubisCO under high-light conditions in the toxic cyanobacterium Microcystis aeruginosa PCC7806

The frequent production of the hepatotoxin microcystin (MC) and its impact on the lifestyle of bloom-forming cyanobacteria are poorly understood. Here, we report that MC interferes with the assembly and the subcellular localization of RubisCO, in Microcystis aeruginosa PCC7806. Immunofluorescence, electron microscopic and cellular fractionation studies revealed a pronounced heterogeneity in the subcellular localization of RubisCO. At high cell density, RubisCO particles are largely separate from carboxysomes in M. aeruginosa and relocate to the cytoplasmic membrane under high-light conditions. We hypothesize that the binding of MC to RubisCO promotes its membrane association and enables an extreme versatility of the enzyme. Steady-state levels of the RubisCO CO₂ fixation product 3-phosphoglycerate are significantly higher in the MC-producing wild type. We also detected noticeable amounts of the RubisCO oxygenase reaction product secreted into the medium that may support the mutual interaction of M. aeruginosa with its heterotrophic microbial community.     

The B-cell antigen receptor signals through a preformed transducer module of SLP65 and CIN85

Spleen tyrosine kinase Syk and its substrate SLP65 (also called BLNK) are proximal signal transducer elements of the B-cell antigen receptor (BCR). Yet, our understanding of signal initiation and processing is limited owing to the incomplete list of SLP65 interaction partners and our ignorance of their association kinetics. We have now determined and quantified the in vivo interactomes of SLP65 in resting and stimulated B cells by mass spectrometry. SLP65 orchestrated a complex signal network of about 30 proteins that was predominantly based on dynamic interactions. However, a stimulation-independent and constant association of SLP65 with the Cbl-interacting protein of 85 kDa (CIN85) was requisite for SLP65 phosphorylation and its inducible plasma membrane translocation. In the absence of a steady SLP65/CIN85 complex, BCR-induced Ca(2+) and NF-κB responses were abrogated. Finally, live cell imaging and co-immunoprecipitation experiments further confirmed that both SLP65 and CIN85 are key components of the BCR-associated primary transducer module required for the onset and progression phases of BCR signal transduction.     

Temporal variation in feeding behaviour and trophic ecology of the temperate hemiramphid, <Emphasis Type="BoldItalic">Hyporhamphus melanochir</Emphasis>

The feeding ecology of southern garfish, Hyporhamphus melanochir, in South Australia was investigated to determine the dietary composition and diurnal feeding patterns, especially in relation to a hypothesised relationship between prey availability and feeding patterns. Samples of H. melanochir were collected at different times of the day and night during autumn and winter, and assigned to 3-hourly intervals. The dietary composition and feeding patterns were determined from gut contents analysis. The main food items were seagrasses (Zosteraceae) and hyperbenthic crustaceans, mainly amphipods. Polychaetes and insects were also consumed. A clear diurnal trophic shift was evident: seagrass was consumed in large volumes during the day, whilst hyperbenthic invertebrates dominated the diet during the night. Plankton samples indicated that this trophic shift reflected the higher abundances of hyperbenthic invertebrates in the water column at night. Less time was spent consuming seagrass during winter, coinciding with shorter day-lengths. H. melanochir has a strong trophic association with seagrass beds, which may account for the high garfish abundance in northern Gulf St. Vincent where extensive Zosteracean seagrass beds occur. This may be useful fundamental information for future environmentally-based fishery management decisions to help ensure the sustainability of southern garfish population and the ecosystem of which it is a part.     

A mannan binding lectin is involved in cell-cell attachment in a toxic strain of Microcystis aeruginosa

Microcystin, a hepatotoxin that represents a serious health risk for humans and livestock, is produced by the bloom-forming cyanobacterium Microcystis aeruginosa in freshwater bodies worldwide. Here we describe the discovery of a lectin, microvirin (MVN), in M. aeruginosa PCC7806 that shares 33% identity with the potent anti-HIV protein cyanovirin-N from Nostoc ellipsosporum. Carbohydrate microarrays were employed to demonstrate the high specificity of the protein for high-mannose structures containing alpha(1-->2) linked mannose residues. Lectin binding analyses and phenotypic characterizations of MVN-deficient mutants suggest that MVN is involved in cell-cell recognition and cell-cell attachment of Microcystis. A binding partner of MVN was identified in the lipopolysaccharide fraction of M. aeruginosa PCC7806. MVN is differentially expressed in mutants lacking the hepatotoxin microcystin. Additionally, MVN-deficient mutants contain much lower amounts of microcystin than the wild-type cells. We discuss a possible functional correlation between microcystin and the lectin and possible implications on Microcystis morphotype formation. This study provides the first experimental evidence that microcystins may have an impact on Microcystis colony formation that is highly important for the competitive advantage of Microcystis over other phytoplankton species.