Podcasts about anabaena

Plants can't do it all by themselves. In order to get the most out of the soil and, indeed, the air, most plants form symbiotic relationships with bacteria and fungi. We take a look at Anabaena, root nodules, and mycorrhizae. Roots are often modified to form "survival structures" containing sugars or proteins. Carrots, cassava, batata and yam are typical examples that are used as food sources by humans. In the last part of this lecture we briefly touch on global and local soil problems like erosion, lack of nutrients, and excess of minerals that increases soil toxicity. Copyright 2012 La Trobe University, all rights reserved. Contact for permissions.

Plants can't do it all by themselves. In order to get the most out of the soil and, indeed, the air, most plants form symbiotic relationships with bacteria and fungi. We take a look at Anabaena, root nodules, and mycorrhizae. Roots are often modified to form "survival structures" containing sugars or proteins. Carrots, cassava, batata and yam are typical examples that are used as food sources by humans. In the last part of this lecture we briefly touch on global and local soil problems like erosion, lack of nutrients, and excess of minerals that increases soil toxicity. Copyright 2012 La Trobe University, all rights reserved. Contact for permissions.

To become biologically active, a protein must fold into a distinct three-dimensional structure. Many non-native proteins require molecular chaperones to support folding and assembly. These molecular chaperones are important for de novo protein folding as well as refolding of denatured proteins under stress conditions. A certain subset of chaperones, the chaperonins, are required for the folding of the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco); furthermore, correct folding of Rubisco is also aided by the Hsp70 chaperone system. Rubisco catalyzes the initial step of CO2 assimilation in the Calvin-Benson-Bassham (CBB) cycle. Unfortunately, this enzyme is extremely inefficient, not only does it exhibit a slow catalytic rate (three CO2 molecules fixed per second per Rubisco) but it also discriminates poorly between the assimilation of CO2 and O2 to its sugar-phosphate substrate ribulose-1,5-bisphosphate (RuBP), the latter resulting in loss of photosynthetic efficiency. Due to these inefficiencies, carbon fixation by Rubisco is the rate limiting step of the CBB cycle. Photosynthetic organisms must produce tremendous amounts of Rubisco to alleviate these shortcomings; therefore significant quantities of nitrogen stores are invested in the production of Rubisco making Rubisco the most abundant protein on earth. These drawbacks of Rubisco have important implications in increasing CO2 concentrations and temperatures in the context of global warming. The ability to engineer a more efficient Rubisco could potentially reduce photosynthetic water usage, increase plant growth yield, and reduce nitrogen usage is plants. However, eukaryotic Rubisco cannot fold and assemble outside of the chloroplast, hindering advancements in creating a more efficient Rubisco. Form I Rubisco, found in higher plants, algae, and cyanobacteria, is a hexadecameric complex consisting of a core of eight ~50 kDa large subunits (RbcL), which is capped by four ~15 kDa small subunits (RbcS) on each end. The discovery of a Rubisco-specific assembly chaperone, RbcX, has lead to a better understanding of the components necessary for the form I Rubisco assembly process. RbcX is a homodimer of ~15 kDa subunits consisting of four α- helices aligned in an anti-parallel fashion along the α4 helix. RbcX2 functions as a stabilizer of folded RbcL by recognizing a highly conserved C-terminal sequence of RbcL: EIKFEFD, termed the C-terminal recognition motif. As has been demonstrated by studies of cyanobacterial Rubisco, de novo synthesized RbcL is folded by the chaperonins, whereupon RbcX2 stabilizes the folded RbcL monomer upon release from the folding cavity and then assists in the formation of the RbcL8 core. RbcX2 forms a dynamic complex with RbcL8 and as a result, RbcX2 is readily displaced by RbcS docking in an ATP-independent manner, thereby creating the functional holoenzyme. However, the exact mechanism by which RbcS binding displaces RbcX2 from the RbcL8 core is still unknown. Furthermore, though much advancement has been made in the understanding of form I Rubisco folding and assembly, an exact and detailed mechanism of form I Rubisco assembly is still lacking. The highly dynamic complex of RbcL/RbcX is critical for the formation of the holoenzyme; however it has hindered attempts to characterize critical regions of RbcL that interact with the peripheral regions of RbcX2. An important observation arose when heterologous RbcL and RbcX2 components interacted; a stable complex could form enabling in depth characterization of the RbcL/RbcX2 interaction. In the present study, the detailed structural mechanism of RbcX2-mediated cyanobacterial form I Rubisco assembly is elucidated. To obtain molecular insight into the RbcX2-mediated assembly process of cyanobacterial form I Rubisco, cryo-EM and crystallographic studies in concert with mutational analysis were employed by taking advantage of the high affinity interaction between RbcL and RbcX2 in the heterologous system (Synechococcus sp. PCC6301 RbcL and Anabaena sp. CA RbcX2). Structure guided mutational analysis based on the 3.2 Å crystal structure of the RbcL8/(RbcX2)8 assembly intermediate were utilized to determine the precise interaction site between the body of RbcL and the peripheral region of RbcX2. From these studies a critical salt bridge could be identified that functions as a guidepoint for correct dimer formation, and it was observed that RbcX2 exclusively mediates Rubisco dimer assembly. Furthermore, the mechanism of RbcX2 displacement from the RbcL8 core by RbcS binding was elucidated as well as indications of how RbcS docking on the RbcL8 core is imperative for full form I Rubisco catalytic function by stabilizing the enzymatically competent conformation of an N-terminal loop of Rubisco termed the ‘60ies loop’. Finally, initial attempts in in vitro reconstitution of eukaryotic Rubisco are reported along with the characterization of Arabidopsis thaliana RbcX2 binding to the C-terminal recognition motif of the Rubisco large subunit from various species.

The filamentous cyanobacterium Anabaena sp. PCC 7120 (further referred to as Anabaena sp.) is a model system to study nitrogen fixation, cell differentiation, cell pattern formation and evolution of plastids. It is a multicellular photosynthetic microorganism consisting of two cell types, vegetative cells and nitrogen fixing heterocysts. This study focuses on the function and dynamics of the proteome of the Gram-negative outer membrane in Anabaena sp. with emphasis on cell differentiation and iron limitation. The newly developed methods for the membrane fractionation are presented, followed by analysis and comparison of the outer membrane proteomes of vegetative cells and heterocysts. The absence of major proteomic alterations in the outer membrane between two cell types, together with the presented data on GFP activity in mutant strains, experimentally support the previously proposed continuum of the outer membrane and the periplasm in Anabaena sp. filament. Also, somewhat different properties of the Anabaena sp. periplasm than in unicellular cyanobacteria are suggested. Furthermore, two common classes of the outer membrane -barrel proteins are analyzed closer. First, Alr2887 protein, as shown here, is a TolC homologue present in both cell types. Protein secretion through Alr2887 / TolC channel-tunnel is essential for the heterocysts maturation and the glycolipid layer formation. Furthermore, the inner membrane ABC transporter encoded by devBCA operon is proposed as component of the TolC efflux system in Anabaena sp. heterocysts. Second, phylogenetic analysis of the surprisingly abundant protein family of 24 TonB-dependent iron transporters in Anabaena sp. is presented. Five members of this family are detected in the outer membrane of vegetative cells under iron-repletion and two of them, All4026 and Alr0397, are explored closer. It is demonstrated that the function of these iron transporters is required for maintaining iron homeostasis of the filaments under iron-replete conditions. Consequently, their gene expression is constant and not enhanced by iron limitation. All4026 and Alr0397 have different specificity for siderophore substrates and in addition to iron transport, All4026 protein is capable of copper uptake and influence on copper homeostasis in Anabaena sp. as well.