Energy and electron transfer in photosystem II of a chlorophyll b-containing Synechocystis sp. PCC 6803 mutant

Using a Synechocystis sp. PCC 6803 mutant strain that lacks photosystem (PS) I and that synthesizes chlorophyll (Chl) b, a pigment that is not naturally present in the wild-type cyanobacterium, the functional consequences of incorporation of this pigment into the PS II core complex were investigated. Despite substitution of up to 75% of the Chl a in the PS II core complex by Chl b, the modified PS II centers remained essentially functional and were able to oxidize water and reduce Q(A), even upon selective excitation of Chl b at 460 nm. Time-resolved fluorescence decay measurements upon Chl excitation showed a significant reduction in the amplitude of the 60-70 ps component of fluorescence decay in open Chl b-containing PS II centers. This may indicate slower energy transfer from the PS II core antenna to the reaction center pigments or slower energy trapping. Chl b and pheophytin b were present in isolated PS II reaction centers. Pheophytin b can be reversibly photoreduced, as evidenced from the absorption bleaching at approximately 440 and 650 nm upon illumination in the presence of dithionite. Upon excitation at 685 nm, transient absorption measurements using PS II particles showed some bleaching at 650 nm together with a major decrease in absorption around 678 nm. The 650 nm bleaching that developed within approximately 10 ps after the flash and then remained virtually unchanged for up to 1 ns was attributed to formation of reduced pheophytin b and oxidized Chl b in some PS II reaction centers. Chl b-containing PS II had a lower rate of charge recombination of Q(A)(-) with the donor side and a significantly decreased yield of delayed luminescence in the presence of DCMU. Taken together, the data suggest that Chl b and pheophytin b participate in electron-transfer reactions in PS II reaction centers of Chl b-containing mutant of Synechocystis without significant impairment of PS II function.     

Succinate:quinol oxidoreductases in the cyanobacterium synechocystis sp. strain PCC 6803: presence and function in metabolism and electron transport

The open reading frames sll1625 and sll0823, which have significant sequence similarity to genes coding for the FeS subunits of succinate dehydrogenase and fumarate reductase, were deleted singly and in combination in the cyanobacterium Synechocystis sp. strain PCC 6803. When the organic acid content in the Deltasll1625 and Deltasll0823 strains was analyzed, a 100-fold decrease in succinate and fumarate concentrations was observed relative to the wild type. A similar analysis for the Deltasll1625 Deltasll0823 strain revealed that 17% of the wild-type succinate levels remained, while only 1 to 2% of the wild-type fumarate levels were present. Addition of 2-oxoglutarate to the growth media of the double mutant strain prior to analysis of organic acids in cells caused succinate to accumulate. This indicates that succinate dehydrogenase activity had been blocked by the deletions and that 2-oxoglutarate can be converted to succinate in vivo in this organism, even though a traditional 2-oxoglutarate dehydrogenase is lacking. In addition, reduction of the thylakoid plastoquinone pool in darkness in the presence of KCN was up to fivefold slower in the mutants than in the wild type. Moreover, in vitro succinate dehydrogenase activity observed in wild-type membranes is absent from those isolated from the double mutant and reduced in those from the single mutants, further indicating that the sll1625 and sll0823 open reading frames encode subunits of succinate dehydrogenase complexes that are active in the thylakoid membrane of the cyanobacterium.     

Systems analysis of primary Sjögren's syndrome pathogenesis in salivary glands identifies shared pathways in human and a mouse model

Bone tissue has an exceptional quality to regenerate to native tissue in response to injury. However, the fracture repair process requires mechanical stability or a viable biological microenvironment or both to ensure successful healing to native tissue. An improved understanding of the molecular and cellular events that occur during bone repair and remodeling has led to the development of biologic agents that can augment the biological microenvironment and enhance bone repair. Orthobiologics, including stem cells, osteoinductive growth factors, osteoconductive matrices, and anabolic agents, are available clinically for accelerating fracture repair and treatment of compromised bone repair situations like delayed unions and nonunions. Preclinical and clinical studies using biologic agents like recombinant bone morphogenetic proteins have demonstrated an efficacy similar or better than that of autologous bone graft in acute fracture healing. A lack of standardized outcome measures for comparison of biologic agents in clinical fracture repair trials, frequent off-label use, and a limited understanding of the biological activity of these agents at the bone repair site have limited their efficacy in clinical applications.     

Evolution of body condition‐dependent dispersal in metapopulations

Body condition‐dependent dispersal strategies are common in nature. Although it is obvious that environmental constraints may induce a positive relationship between body condition and dispersal, it is not clear whether positive body conditional dispersal strategies may evolve as a strategy in metapopulations. We have developed an individual‐based simulation model to investigate how body condition–dispersal reaction norms evolve in metapopulations that are characterized by different levels of environmental stochasticity and dispersal mortality. In the model, body condition is related to fecundity and determined either by environmental conditions during juvenile development (adult dispersal) or by those experienced by the mother (natal dispersal). Evolutionarily stable reaction norms strongly depend on metapopulation conditions: positive body condition dependency of dispersal evolved in metapopulation conditions with low levels of dispersal mortality and high levels of environmental stochasticity. Negative body condition‐dependent dispersal evolved in metapopulations with high dispersal mortality and low environmental stochasticity. The latter strategy is responsible for higher dispersal rates under kin competition when dispersal decisions are based on body condition reached at the adult life stage. The evolution of both positive and negative body condition‐dependent dispersal strategies is consequently likely in metapopulations and depends on the prevalent environmental conditions.     

Open reading frame ssr2016 is required for antimycin A-sensitive photosystem I-driven cyclic electron flow in the cyanobacterium Synechocystis sp. PCC 6803

Open reading frame ssr2016 encodes a protein with substantial sequence similarities to PGR5 identified as a component of the antimycin A-sensitive ferredoxin:plastoquinone reductase (FQR) in PSI cyclic photophosphorylation in Arabidopsis thaliana. We studied cyclic electron flow in Synechocystis sp. PCC 6803 in vivo in ssr2016 deletion mutants generated either in a wild-type background or in a ndhB deletion mutant. Our results indicate that ssr2016 is required for FQR and that it operates in a parallel pathway to the NDH1 complex. The ssr2016 deletion mutants are high light sensitive, suggesting that FQR might be important in controlling redox poise under adverse conditions.     

CHARMM-GUI HMMM Builder for Membrane Simulations with the Highly Mobile Membrane-Mimetic Model

Slow diffusion of the lipids in conventional all-atom simulations of membrane systems makes it difficult to sample large rearrangements of lipids and protein-lipid interactions. Recently, Tajkhorshid and co-workers developed the highly mobile membrane-mimetic (HMMM) model with accelerated lipid motion by replacing the lipid tails with small organic molecules. The HMMM model provides accelerated lipid diffusion by one to two orders of magnitude, and is particularly useful in studying membrane-protein associations. However, building an HMMM simulation system is not easy, as it requires sophisticated treatment of the lipid tails. In this study, we have developed CHARMM-GUI HMMM Builder (http://www.charmm-gui.org/input/hmmm) to provide users with ready-to-go input files for simulating HMMM membrane systems with/without proteins. Various lipid-only and protein-lipid systems are simulated to validate the qualities of the systems generated by HMMM Builder with focus on the basic properties and advantages of the HMMM model. HMMM Builder supports all lipid types available in CHARMM-GUI and also provides a module to convert back and forth between an HMMM membrane and a full-length membrane. We expect HMMM Builder to be a useful tool in studying membrane systems with enhanced lipid diffusion.     

Mossbauer spectroscopy of cells of cyanobacteria Synechocystis sp. PCC 6803 devoid of photosystem I and containing inactive phycobilisomes]

Mossbauer spectra of the psaAB mutant of Synechocystis sp. PPC 6803 devoid of photosystem I grown in a 57Fe-containing medium were measured. The spectrum is a broadened doublet whose size (about 20%) and parameters (isomeric shift delta = 0.3 mm/s and quadrupole splitting delta = 0.8 mm/s) suggest the presence of abundant nanoclusters of Fe3+ oxides in a superparamagnetic state tightly bound to the membrane. Treatment of cells with EDTA was accompanied by a substantial (tenfold) decrease in the amount of iron nonspecifically bound to the membrane and the appearance of Fe2+ localized, probably, inside cells and/or cell membranes. In addition, the spectrum of washed cells exhibited superfine magnetic splitting due to iron oxide clusters greater in size than nanoclusters present in the membrane prior to EDTA treatment.     

Biological controls upon the physical taphonomy of exceptionally preserved salamanders from the Miocene of Rubielos de Mora,northeast Spain

McNamara, M.E., Orr, P.J., Manzocchi, T., Alcalá, L., Anadón, P. & Peñalver, E. 2011: Biological controls upon the physical taphonomy of exceptionally preserved salamanders from the Miocene of Rubielos de Mora, northeast Spain. Lethaia, Vol. 45, pp. 210–226. The middle Miocene Rubielos de Mora Konservat‐Lagerstätte of northeast Spain is hosted within profundal, finely laminated, lacustrine mudstones. The diverse biota includes abundant salamanders. Most individuals died during separate episodes and sank rapidly postmortem. Specimens are typically preserved in dorso‐ventral aspect, the most hydrodynamically stable orientation. The near‐cylindrical morphology of the body, however, allowed some carcasses to settle in or subsequently re‐orientate into, lateral orientations. Loss of skeletal elements (i.e. reduced completeness) reflects their location within the body and followed a distal to proximal trend. Two stages are identified: initial loss of a small number of phalanges, followed by loss of more proximal limb bones plus additional phalanges. Disarticulation is more complex: it occurred via several mechanisms (notably, abdominal rupture and re‐orientation of part of the body and limbs during decay) and shows no consistent pattern among specimens. The physical taphonomy of the salamanders is controlled predominantly by intrinsic biological factors, i.e. the geometry of the body and of individual skeletal elements, the orientation, inherent strength and location of specific joints and the extent to which soft tissues, particularly the skin, persist during decay. These biological factors probably control patterns of physical taphonomy of other fossil tetrapods with a similar skeletal configuration. □Articulation, completeness, Konservat‐Lagerstätten, orientation, quantitative taphonomy, salamanders.     

The zeaxanthin biosynthesis enzyme beta-carotene hydroxylase is involved in myxoxanthophyll synthesis in Synechocystis sp. PCC 6803.

Beta-carotene hydroxylase is known to be involved in zeaxanthin synthesis. Disruption of the crtR gene encoding beta-carotene hydroxylase in Synechocystis sp. PCC 6803 resulted in the absence of both zeaxanthin synthesis and myxoxanthophyll accumulation in the mutant strain. A new carotenoid was detected in this strain. Its chemical structure was close to that of myxoxanthophyll, but the hydroxyl group on the beta-ring was lacking. This compound, deoxy-myxoxanthophyll, most likely is an intermediate in the myxoxanthophyll biosynthesis pathway. Therefore, beta-carotene hydroxylase is involved not only in zeaxanthin synthesis but also in myxoxanthophyll synthesis in Synechocystis. Furthermore, myxoxanthophyll in Synechocystis was found to have a higher molecular mass than what was determined in other species. This difference is likely to be due to a difference in the sugar moiety.