Effect of Dehydrated Trehalose Matrix on the Kinetics of Forward Electron Transfer Reactions in Photosystem I

The effect of dehydration on the kinetics of forward electron transfer (ET) has been studied in cyanobacterial photosystem I (PS I) complexes in a trehalose glassy matrix by time-resolved optical and EPR spectroscopies in the 100 fs to 1 ms time domain. The kinetics of the flash-induced absorption changes in the subnanosecond time domain due to primary and secondary charge separation steps were monitored by pump–probe laser spectroscopy with 20-fs low-energy pump pulses centered at 720 nm. The back-reaction kinetics of P700 were measured by high-field time-resolved EPR spectroscopy and the forward kinetics of A∙−1A/A∙−1B→FX by time-resolved optical spectroscopy at 480 nm. The kinetics of the primary ET reactions to form the primary P∙+700A∙−0 and the secondary P∙+700A∙−1 ion radical pairs were not affected by dehydration in the trehalose matrix, while the yield of the P∙+700A∙−1 was decreased by ~20%. Forward ET from the phylloquinone molecules in the A∙−1A and A∙−1B sites to the iron–sulfur cluster FX slowed from ~220 ns and ~20 ns in solution to ~13 μs and ~80 ns, respectively. However, as shown by EPR spectroscopy, the ~15 μs kinetic phase also contains a small contribution from the recombination between A∙−1B and P∙+700. These data reveal that the initial ET reactions from P700 to secondary phylloquinone acceptors in the A- and B-branches of cofactors (A1A and A1B) remain unaffected whereas ET beyond A1A and A1B is slowed or prevented by constrained protein dynamics due to the dry trehalose glass matrix

Electrogenic reduction of the primary electron donor P700+ in photosystem I by redox dyes

AbstractThe kinetics of reduction of the photo-oxidized primary electron donor P700+ by redox dyes N,N,N′,N′-tetramethyl-p-phenylendiamine, 2,6-dichlorophenol-indophenol and phenazine methosulfate was studied in proteoliposomes containing Photosystem I complexes from cyanobacteria Synechocystis sp. PCC 6803 using direct electrometrical technique. In the presence of high concentrations of redox dyes, the fast generation of a membrane potential related to electron transfer between P700 and the terminal iron-sulfur clusters FA/FB was followed by a new electrogenic phase in the millisecond time domain, which contributes approximately 20% to the overall photoelectric response. This phase is ascribed to the vectorial transfer of an electron from the redox dye to the protein-embedded chlorophyll of P700+. Since the contribution of this electrogenic phase in the presence of artificial redox dyes is approximately equal to that of the phase observed earlier in the presence of cytochrome c6, it is likely that electrogenic reduction of P700+ in vivo occurs due to vectorial electron transfer within RC molecule rather than within the cytochrome c6-P700 complex

Incorporation of a high potential quinone reveals that electron transfer in Photosystem I becomes highly asymmetric at low temperature

Photosystem I (PS I) has two nearly identical branches of electron-transfer co-factors. Based on point mutation studies, there is general agreement that both branches are active at ambient temperature but that the majority of electron-transfer events occur in the A-branch. At low temperature, reversible electron transfer between P700 and A1A occurs in the A-branch. However, it has been postulated that irreversible electron transfer from P700 through A1B to the terminal iron-sulfur clusters FA and FB occurs via the B-branch. Thus, to study the directionality of electron transfer at low temperature, electron transfer to the iron-sulfur clusters must be blocked. Because the geometries of the donor–acceptor radical pairs formed by electron transfer in the A- and B-branch differ, they have different spin-polarized EPR spectra and echo- modulation decay curves. Hence, time-resolved, multiple-frequency EPR spectroscopy, both in the direct-detection and pulse mode, can be used to probe the use of the two branches if electron transfer to the iron-sulfur clusters is blocked. Here, we use the PS I variant from the menB deletion mutant strain of Synechocyctis sp. PCC 6803, which is unable to synthesize phylloquinone, to incorporate 2,3-dichloro-1,4-naphthoquinone (Cl2NQ) into the A1A and A1B binding sites. The reduction midpoint potential of Cl2NQ is approximately 400 mV more positive than that of phylloquinone and is unable to transfer electrons to the iron-sulfur clusters. In contrast to previous studies, in which the iron-sulfur clusters were chemically reduced and/or point mutations were used to prevent electron transfer past the quinones, we find no evidence for radical-pair formation in the B-branch. The implications of this result for the directionality of electron transfer in PS I are discussed

Structure of a dimeric photosystem II complex from a cyanobacterium acclimated to far-red light

Photosystem II (PSII) is the water-splitting enzyme central to oxygenic photosynthesis. To drive water oxidation, light is harvested by accessory pigments, mostly chlorophyll (Chl) a molecules, which absorb visible light (400–700 nm). Some cyanobacteria facultatively acclimate to shaded environments by altering their photosynthetic machinery to additionally absorb far-red light (FRL, 700–800 nm), a process termed far-red light photoacclimation or FaRLiP. During far-red light photoacclimation, FRL-PSII is assembled with FRL-specific isoforms of the subunits PsbA, PsbB, PsbC, PsbD, and PsbH, and some Chl-binding sites contain Chls d or f instead of the usual Chl a. The structure of an apo-FRL-PSII monomer lacking the FRL-specific PsbH subunit has previously been determined, but visualization of the dimeric complex has remained elusive. Here, we report the cryo-EM structure of a dimeric FRL–PSII complex. The site assignments for Chls d and f are consistent with those assigned in the previous apo-FRL-PSII monomeric structure. All sites that bind Chl d or Chl f at high occupancy exhibit a FRL-specific interaction of the formyl moiety of the Chl d or Chl f with the protein environment, which in some cases involves a phenylalanine sidechain. The structure retains the FRL-specific PsbH2 subunit, which appears to alter the energetic landscape of FRL-PSII, redirecting energy transfer from the phycobiliprotein complex to a Chl f molecule bound by PsbB2 that acts as a bridge for energy transfer to the electron transfer chain. Collectively, these observations extend our previous understanding of the structure-function relationship that allows PSII to function using lower energy FRL

Light-driven chloride transport kinetics of halorhodopsin

Despite growing interest in light-driven ion pumps for use in optogenetics, current estimates of their transport rates span two orders of magnitude due to challenges in measuring slow transport processes and determining protein concentration and/or orientation in membranes in vitro. In this study, we report, to our knowledge, the first direct quantitative measurement of light-driven Cl transport rates of the anion pump halorohodopsin from Natronomonas pharaonis (NpHR). We used light-interfaced voltage clamp measurements on NpHR-expressing oocytes to obtain a transport rate of 219 (± 98) Cl /protein/s for a photon flux of 630 photons/protein/s. The measurement is consistent with the literature-reported quantum efficiency of ∼30% for NpHR, i.e., 0.3 isomerizations per photon absorbed. To reconcile our measurements with an earlier-reported 20 ms rate-limiting step, or 35 turnovers/protein/s, we conducted, to our knowledge, novel consecutive single-turnover flash experiments that demonstrate that under continuous illumination, NpHR bypasses this step in the photocycle

Characterization of chlorophyll f synthase heterologously produced in Synechococcus sp. PCC 7002.

In diverse terrestrial cyanobacteria, Far-Red Light Photoacclimation (FaRLiP) promotes extensive remodeling of the photosynthetic apparatus, including photosystems (PS)I and PSII and the cores of phycobilisomes, and is accompanied by the concomitant biosynthesis of chlorophyll (Chl) d and Chl f. Chl f synthase, encoded by chlF, is a highly divergent paralog of psbA; heterologous expression of chlF from Chlorogloeopsis fritscii PCC 9212 led to the light-dependent production of Chl f in Synechococcus sp. PCC 7002 (Ho et al., Science 353, aaf9178 (2016)). In the studies reported here, expression of the chlF gene from Fischerella thermalis PCC 7521 in the heterologous system led to enhanced synthesis of Chl f. N-terminally [His]10-tagged ChlF7521 was purified and identified by immunoblotting and tryptic-peptide mass fingerprinting. As predicted from its sequence similarity to PsbA, ChlF bound Chl a and pheophytin a at a ratio of ~ 3-4:1, bound β-carotene and zeaxanthin, and was inhibited in vivo by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Cross-linking studies and the absence of copurifying proteins indicated that ChlF forms homodimers. Flash photolysis of ChlF produced a Chl a triplet that decayed with a lifetime (1/e) of ~ 817 µs and that could be attributed to intersystem crossing by EPR spectroscopy at 90 K. When the chlF7521 gene was expressed in a strain in which the psbD1 and psbD2 genes had been deleted, significantly more Chl f was produced, and Chl f levels could be further enhanced by specific growth-light conditions. Chl f synthesized in Synechococcus sp. PCC 7002 was inserted into trimeric PSI complexes

TWIN: Personality-based Intelligent Recommender System

This paper presents the Tell me What I Need (TWIN) Personality-based Intelligent Recommender System, the goal of which is to recommend items chosen by like-minded (or twin ) people with similar personality types which we estimate from their writings. In order to produce recommendations it applies the results achieved in the personality from the text recognition research field to Personality-based Recommender System user profile modelling. In this way it creates a bridge between the efforts of automatic personality score estimation from plain text and the field of Intelligent Recommender Systems. The paper describes the TWIN system architecture, and results of the experimentation with the system in the online travelling domain in order to investigate the possibility of providing valuable recommendations of hotels of the TripAdvisor website for like-minded people . The results compare favourably with related experiments, although they demonstrate the complexity of this challenging task.The research work of the third author is partially funded by the WIQ-EI (IRSES grant n. 269180) and DIANA APPLICATIONS (TIN2012-38603-C02-01), and done in the framework of the VLC/Campus Microcluster on Multimodal Interaction in Intelligent Systems.Roshchina, A.; Cardiff, J.; Rosso, P. (2015). TWIN: Personality-based Intelligent Recommender System. Journal of Intelligent and Fuzzy Systems. 28(5):2059-2071. https://doi.org/10.3233/IFS-141484S20592071285Bodapati, A. V. (2008). Recommendation Systems with Purchase Data. Journal of Marketing Research, 45(1), 77-93. doi:10.1509/jmkr.45.1.77Dean, J., & Ghemawat, S. (2008). MapReduce. Communications of the ACM, 51(1), 107. doi:10.1145/1327452.1327492Nageswara Rao, K. (2008). Application Domain and Functional Classification of Recommender Systems—A Survey. DESIDOC Journal of Library & Information Technology, 28(3), 17-35. doi:10.14429/djlit.28.3.174Castro, J., Rodriguez, R. M., & Barranco, M. J. (2013). Weighting of Features in Content-Based Filtering with Entropy and Dependence Measures. International Journal of Computational Intelligence Systems, 7(1), 80-89. doi:10.1080/18756891.2013.859861Cantador, I., Bellogín, A., & Vallet, D. (2010). Content-based recommendation in social tagging systems. Proceedings of the fourth ACM conference on Recommender systems - RecSys ’10. doi:10.1145/1864708.1864756Huang, S. (2011). Designing utility-based recommender systems for e-commerce: Evaluation of preference-elicitation methods. Electronic Commerce Research and Applications, 10(4), 398-407. doi:10.1016/j.elerap.2010.11.003Tkalčič, M., Burnik, U., & Košir, A. (2010). Using affective parameters in a content-based recommender system for images. User Modeling and User-Adapted Interaction, 20(4), 279-311. doi:10.1007/s11257-010-9079-zRentfrow, P. J., & Gosling, S. D. (2003). The do re mi’s of everyday life: The structure and personality correlates of music preferences. Journal of Personality and Social Psychology, 84(6), 1236-1256. doi:10.1037/0022-3514.84.6.1236Elahi, M., Braunhofer, M., Ricci, F., & Tkalcic, M. (2013). Personality-Based Active Learning for Collaborative Filtering Recommender Systems. Lecture Notes in Computer Science, 360-371. doi:10.1007/978-3-319-03524-6_31Tkalcic, M., Odic, A., Kosir, A., & Tasic, J. (2013). Affective Labeling in a Content-Based Recommender System for Images. IEEE Transactions on Multimedia, 15(2), 391-400. doi:10.1109/tmm.2012.2229970Quercia, D., Kosinski, M., Stillwell, D., & Crowcroft, J. (2011). Our Twitter Profiles, Our Selves: Predicting Personality with Twitter. 2011 IEEE Third Int’l Conference on Privacy, Security, Risk and Trust and 2011 IEEE Third Int’l Conference on Social Computing. doi:10.1109/passat/socialcom.2011.26Mairesse, F., Walker, M. A., Mehl, M. R., & Moore, R. K. (2007). Using Linguistic Cues for the Automatic Recognition of Personality in Conversation and Text. Journal of Artificial Intelligence Research, 30, 457-500. doi:10.1613/jair.2349Golbeck, J., Robles, C., & Turner, K. (2011). Predicting personality with social media. Proceedings of the 2011 annual conference extended abstracts on Human factors in computing systems - CHI EA ’11. doi:10.1145/1979742.1979614Hall, M., Frank, E., Holmes, G., Pfahringer, B., Reutemann, P., & Witten, I. H. (2009). The WEKA data mining software. ACM SIGKDD Explorations Newsletter, 11(1), 10. doi:10.1145/1656274.1656278Tausczik, Y. R., & Pennebaker, J. W. (2009). The Psychological Meaning of Words: LIWC and Computerized Text Analysis Methods. Journal of Language and Social Psychology, 29(1), 24-54. doi:10.1177/0261927x09351676Islam, M. J., Wu, Q. M. J., Ahmadi, M., & Sid-Ahmed, M. A. (2007). Investigating the Performance of Naive- Bayes Classifiers and K- Nearest Neighbor Classifiers. 2007 International Conference on Convergence Information Technology (ICCIT 2007). doi:10.1109/iccit.2007.14

Development and validation of the Diabetes Numeracy Test (DNT)

<p>Abstract</p> <p>Background</p> <p>Low literacy and numeracy skills are common. Adequate numeracy skills are crucial in the management of diabetes. Diabetes patients use numeracy skills to interpret glucose meters, administer medications, follow dietary guidelines and other tasks. Existing literacy scales may not be adequate to assess numeracy skills. This paper describes the development and psychometric properties of the Diabetes Numeracy Test (DNT), the first scale to specifically measure numeracy skills used in diabetes.</p> <p>Methods</p> <p>The items of the DNT were developed by an expert panel and refined using cognitive response interviews with potential respondents. The final version of the DNT (43 items) and other relevant measures were administered to a convenience sample of 398 patients with diabetes. Internal reliability was determined by the Kuder-Richardson coefficient (KR-20). An <it>a priori </it>hypothetical model was developed to determine construct validity. A shortened 15-item version, the DNT15, was created through split sample analysis.</p> <p>Results</p> <p>The DNT had excellent internal reliability (KR-20 = 0.95). The DNT was significantly correlated (p < 0.05) with education, income, literacy and math skills, and diabetes knowledge, supporting excellent construct validity. The mean score on the DNT was 61% and took an average of 33 minutes to complete. The DNT15 also had good internal reliability (KR-20 = 0.90 and 0.89). In split sample analysis, correlations of the DNT-15 with the full DNT in both sub-samples was high (rho = 0.96 and 0.97, respectively).</p> <p>Conclusion</p> <p>The DNT is a reliable and valid measure of diabetes related numeracy skills. An equally adequate but more time-efficient version of the DNT, the DNT15, can be used for research and clinical purposes to evaluate diabetes related numeracy.</p