Investigating the structure and function of the FtsH protease family in Synechocystis sp. PCC 6803

FtsH proteases are found throughout nature and contain a conserved ATPase domain, flanked by an N-terminal transmembrane domain and a Zn2+-binding protease domain. They play diverse roles in maintaining cellular activity. In the case of oxygenic photosynthetic organisms, FtsH-mediated degradation of damaged D1 protein is crucial for the operation of the photosystem II repair cycle needed to prevent photoinhibition. Four FtsH homologues are present in the model cyanobacterium Synechocystis sp. PCC 6803. One of these, FtsH2 (Slr0228), is known to be important for D1 degradation. However the structure of the FtsH2 complex is unknown and little is known about the structure and function of the other FtsH homologues. In this work, all four FtsH homologues were isolated via C-terminal GST tagging in tandem with affinity chromatography. Analysis of the purified FtsH complexes revealed the presence of FtsH1(Slr1390)/FtsH3(Slr1604) and FtsH2/FtsH3 heterocomplexes, whereas FtsH4 (Sll1463) appeared to form homocomplexes. Single particle analysis using electron microscopy revealed that the FtsH2-GST/FtsH3 complex was a hexameric particle of diameter ~120 Å with the two types of protomer alternately arranged around the central pore. Inactivation of the protease activity of FtsH2 did not abolish the function of the FtsH2/FtsH3 complex. FtsH2 and FtsH4 are mainly localised in the thylakoid membranes, whereas FtsH3 is dual targeted to both thylakoid and cytoplasmic membranes. FtsH1 is likely to be present in the cytoplasmic membrane. In vitro studies of E. coli over-expressed cytosolic domains of FtsH from Thermosynechococcus elongatus confirmed that the FtsH2, FtsH3 and FtsH4 homologues exhibited both ATPase and CTPase activity but that only FtsH4 could degrade casein. Homologues of E.coli YccA (Sll1150) and Arabidopsis EGY2 (Sll0862) were co-purified with the FtsH2-GST/FtsH3 complex. However, preliminary studies suggest neither is critical for FtsH-mediated D1 degradation. Strikingly, Psb29 (Sll1414) was found to be important for accumulation of FtsH2/FtsH3 complex, but further work is required to determine the mechanism.Open Acces

Who Refers to Whom: A Study of Research References and the Relationship between Research Reports and Final Publication

The size and style of referencing for a large sample of 60 years of publications of the Cowles Foundation are examined. The influence of computerization is considered. Self-referencing is noted and some observations are made on the costs and distribution of research papers.Referencing, Cost of publication

A reversal coarse-grained analysis with application to an altered functional circuit in depression

Introduction: When studying brain function using functional magnetic resonance imaging (fMRI) data containing tens of thousands of voxels, a coarse-grained approach – dividing the whole brain into regions of interest – is applied frequently to investigate the organization of the functional network on a relatively coarse scale. However, a coarse-grained scheme may average out the fine details over small spatial scales, thus rendering it difficult to identify the exact locations of functional abnormalities. Methods: A novel and general approach to reverse the coarse-grained approach by locating the exact sources of the functional abnormalities is proposed. Results: Thirty-nine patients with major depressive disorder (MDD) and 37 matched healthy controls are studied. A circuit comprising the left superior frontal gyrus (SFGdor), right insula (INS), and right putamen (PUT) exhibit the greatest changes between the patients with MDD and controls. A reversal coarse-grained analysis is applied to this circuit to determine the exact location of functional abnormalities. Conclusions: The voxel-wise time series extracted from the reversal coarse-grained analysis (source) had several advantages over the original coarse-grained approach: (1) presence of a larger and detectable amplitude of fluctuations, which indicates that neuronal activities in the source are more synchronized; (2) identification of more significant differences between patients and controls in terms of the functional connectivity associated with the sources; and (3) marked improvement in performing discrimination tasks. A software package for pattern classification between controls and patients is available in Supporting Information

Investor Sentiment and the Mean–Variance Relation

This study shows the influence of investor sentiment on the market\u27s mean–variance tradeoff. We find that the stock market\u27s expected excess return is positively related to the market\u27s conditional variance in low-sentiment periods but unrelated to variance in high-sentiment periods. These findings are consistent with sentiment traders who, during the high-sentiment periods, undermine an otherwise positive mean–variance tradeoff. We also find that the negative correlation between returns and contemporaneous volatility innovations is much stronger in the low-sentiment periods. The latter result is consistent with the stronger positive ex ante relation during such periods

A sentiment-based explanation of the forward premium puzzle

This paper presents a sentiment-based explanation of the forward premium puzzle. Agents over- or underestimate the growth rate of the economy. All else equal, when perceived domestic growth is higher than perceived foreign growth, the domestic interest rate is higher than the foreign interest rate. At the same time, an econometrician would expect an increase in the home currency value. Together, the model with investor misperception can account for the forward premium puzzle.> ; In addition, it helps explain the low correlation of consumption growth differentials and exchange rate growth and the high stock market correlation across countries, despite a low correlation of fundamentals. Finally, this paper provides direct empirical evidence supporting the mechanism in the sentiment-based explanation.Asset pricing ; Foreign exchange ; Financial markets