Cara Tracewell - Academia.edu (original) (raw)

Papers by Cara Tracewell

Structure, May 1, 2004

Secrets of Carotenoid Binding the same manner as the naturally occurring spheroidene in wild-type... more Secrets of Carotenoid Binding the same manner as the naturally occurring spheroidene in wild-type bRCs. Triplet-triplet energy transfer from P to the carotenoid occurs through an accessory bacteriochlorophyll inter-In this issue of Structure, researchers reveal new crysmediate, BChl B. In order for triplet-triplet energy transfer tal structures of the bacterial reaction center of Rb. between two molecules to occur, there must be van sphaeroides R-26.1 containing either no carotenoid or der Waals contact and they must have appropriately natural or synthetic carotenoid (Roszak et al., 2004). matched excited state energy levels. In this study by These structures give insight in to the mechanism of Roszak et al. (2004), in each of the two carotenoid reconcarotenoid binding. stituted bRC X-ray crystal structures, the carotenoid is in van der Waals contact with BChl B. In fact, the position Here, Frank and colleagues (Roszak et al., 2004) report of the 15-15Ј-cis bond of the natural and reconstituted three new X-ray crystallography structures of the bactecarotenoid relative to the BChl B molecule are nearly rial reaction center (bRC) from the carotenoid-less muidentical. In addition to the structural requirement, the tant of Rhodobacter sphaeroides R-26.1 containing eicarotenoid triplet state must be lower in energy than ther no carotenoid or reconstituted with the natural the triplet state of BChl B in order for energy transfer to carotenoid spheroidene or a synthetic carotenoid, 3,4occur. In another study from the Frank laboratory, it was dihydrospheroidene. The structures suggest that acshown that the triplet state on P is not quenched in bRCs cess to the binding site is constrained by the rotational reconstituted with 3,4-dihydrospheroidene (Farhoosh et motion of a phenylalanine residue. Based on this obseral., 1997). Because energy in the excited state flows vation, the authors postulate a mechanism for carotfrom the highest to the lowest energy level, the authors enoid binding which selects for the correct orientation had hypothesized the excited state of 3,4-dihydrospheof the molecule in the bRC. roidene must be higher than the excited state of BChl B. bRCs normally bind a single carotenoid molecule, However, a possibility remained that 3,4-dihydrosphespheroidene. One of the important roles of the carotroidene is not bound to the bRC in the same manner enoid in the bacterial reaction center is to quench triplet as spheroidene. This possibility can now be excluded states that can form on the primary electron donor P because it can be seen in the structure of the bRC as a result of charge recombination reactions (Krinsky, reconstituted with 3,4-dihydrospheroidene that this ca-1971). These bacteriochlorophyll triplet states react with rotenoid does indeed bind in the same position as sphemolecular oxygen to form excited singlet state oxygen, roidene (Roszak et al., 2004). Therefore, this result supwhich can cause oxidative damage to the cell. The carotports the idea that the relatively higher excited state enoid protects the reaction center from oxidative damenergy level of 3,4-dihydrospheroidene compared to age by preventing singlet oxygen formation.

Photosynthesis Research, 2005

Resonance Raman (RR) spectroscopy has been used to examine the configuration of the carotenoids b... more Resonance Raman (RR) spectroscopy has been used to examine the configuration of the carotenoids bound to Synechocystis PCC 6803 Photosystem II (PS II) core complexes. The excitation wavelengths used (514.5, 488.0, 476.5 and 457.9 nm) span the absorption bands of all of the $12-17 neutral carotenoids in the PS II core complex. The RR spectra of the two carotenoids associated with the D1-D2 polypeptides (Car 507 and Car 489) of the reaction center are extracted via light versus dark difference experiments measured at 20 K. The RR results are consistent with all-trans configurations for both Car 507 and Car 489 and indicate that majority of the other carotenoids in the PS II core complex must also be in the all-trans configuration. The configuration of b-carotene is relevant to its proposed function as a molecular wire in the secondary electron-transfer reactions of PS II. Abbreviations: Car 507 and Car 489-carotenoids associated with the D1-D2 polypeptides of the reaction center; Chl-chlorophyll; CP43-chlorophyll-binding protein of molecular weight 43 kDa; CP47-chlorophyll-binding protein of molecular weight 47 kDa; Cyt-cytochrome; b-DMb-dodecyl maltoside; HPLC-high pressure liquid chromatography; MES-2-(N-morpholino)ethanesulphonic acid; PS II-Photosystem II; RC-reaction center; RR-resonance Raman

Biochemistry, Oct 14, 2008

Photosystem II (PS II) is unique among photosynthetic reaction centers in having secondary electr... more Photosystem II (PS II) is unique among photosynthetic reaction centers in having secondary electron donors that compete with the primary electron donors for reduction of P 680 +. We have characterized the photooxidation and dark decay of the redox-active accessory chlorophylls (Chl) and β-carotenes (Car) in oxygen-evolving PS II core complexes by near-IR absorbance and EPR spectroscopies at cryogenic temperatures. In contrast to previous results for Mn-depleted PS II, multiple near-IR absorption bands are resolved in the light-minus-dark difference spectra of oxygen-evolving PS II core complexes including two fast-decaying bands at 793 nm and 814 nm and three slow-decaying bands at 810 nm, 825 nm, and 840 nm. We assign these bands to chlorophyll cation radicals (Chl +). The fast-decaying bands observed after illumination at 20 K could be generated again by reilluminating the sample. Quantization by EPR gives a yield of 0.85 radicals per PS II, and the yield of oxidized cytochrome b 559 by optical difference spectroscopy is 0.15 per PS II. Potential locations of Chl + and Car + species, and the pathways of secondary electron transfer based on the rates of their formation and decay, are discussed. This is the first evidence that Chls in the light-harvesting proteins CP43 and CP47 are oxidized by P 680 + and may have a role in Chl fluorescence quenching. We also suggest that a possible role for negatively charged lipids (phosphatidyldiacylglycerol and sulphoquinovosyldiacylglycerol identified in the PS II structure) could be to decrease the redox potential of specific Chl and Car cofactors. These results provide new insight into the alternate electron-donation pathways to P 680 + .

Archives of Biochemistry and Biophysics, 2001

Carotenoids are known to function as light-harvesting pigments and they play important roles in p... more Carotenoids are known to function as light-harvesting pigments and they play important roles in photoprotection in both plant and bacterial photosynthesis. These functions are also important for carotenoids in photosystem II. In addition, ␤-carotene recently has been found to function as a redox intermediate in an alternate pathway of electron transfer within photosystem II. This redox role of a carotenoid in photosystem II is unique among photosynthetic reaction centers and stems from the very highly oxidizing intermediates that form in the process of water oxidation. In this minireview, an overview of the electron-transfer reactions in photosystem II is presented, with an emphasis on those involving carotenoids. The carotenoid composition of photosystem II and the physical methods used to study the structure of the redox-active carotenoid are reviewed. Possible roles of carotenoid cations in photoprotection of photosystem II are discussed.

Photosynthesis Research, Sep 9, 2008

Beta-carotene (Car) and chlorophyll (Chl) function as secondary electron donors in photosystem II... more Beta-carotene (Car) and chlorophyll (Chl) function as secondary electron donors in photosystem II (PS II) under conditions, such as low temperature, when electron donation from the O(2)-evolving complex is inhibited. In prior studies of the formation and decay of Car(*+) and Chl(*+) species at low temperatures, cytochrome b(559) (Cyt b(559)) was chemically oxidized prior to freezing the sample. In this study, the photochemical formation of Car(*+) and Chl(*+) is characterized at low temperature in O(2)-evolving Synechocystis PS II treated with ascorbate to reduce most of the Cyt b(559). Not all of the Cyt b(559) is reduced by ascorbate; the remainder of the PS II reaction centers, containing oxidized low-potential Cyt b(559), give rise to Car(*+) and Chl(*+) species after illumination at low temperature that are characterized by near-IR spectroscopy. These data are compared to the measurements on ferricyanide-treated O(2)-evolving Synechocystis PS II in which the Car(*+) and Chl(*+) species are generated in PS II centers containing mostly high- and intermediate-potential Cyt b(559). Spectral differences observed in the ascorbate-reduced PS II samples include decreased intensity of the Chl(*+) and Car(*+) absorbance peaks, shifts in the Car(*+) absorbance maxima, and lack of formation of a 750 nm species that is assigned to a Car neutral radical. These results suggest that different spectral forms of Car are oxidized in PS II samples containing different redox forms of Cyt b(559), which implies that different secondary electron donors are favored depending on the redox form of Cytb(559) in PS II.

Journal of Biological Chemistry, Nov 1, 2005

3 The abbreviations used are: PS II, photosystem II; ␤-DM, n-dodecyl-␤-D-maltoside; Car ϩ , carot... more 3 The abbreviations used are: PS II, photosystem II; ␤-DM, n-dodecyl-␤-D-maltoside; Car ϩ , carotenoid radical cation; Car, carotenoid; Chl, chlorophyll; Chl Z , an oxidizable chlorophyll located at the periphery of the PS II reaction center; CP43, chlorophyll-binding protein encoded by psbC; CP47, chlorophyll-binding protein encoded by psbB; CrtI, purple bacterial phytoene desaturase (encoded by crtI); HPLC, high pressure liquid chromatography; MES, 2-(N-morpholino)ethanesulfonic acid; P 680 , first stable electron donor of PS II; Pds, cyanobacterial phytoene desaturase (encoded by crtP or pds); Q A , primary quinone electron acceptor; Q B , secondary quinone electron acceptor; WT, wild type; Zds, cyanobacterial-carotene desaturase (encoded by crtQ or zds); Cyt b 559 , cytochrome b 559 .

Biochemistry, Jul 11, 2003

Photosystem II (PS II) contains secondary electron-transfer paths involving cytochrome b 559 (Cyt... more Photosystem II (PS II) contains secondary electron-transfer paths involving cytochrome b 559 (Cyt b 559), chlorophyll (Chl), and-carotene (Car) that are active under conditions when oxygen evolution is blocked such as in inhibited samples or at low temperature. Intermediates of the secondary electrontransfer pathways of PS II core complexes from Synechocystis PCC 6803 and Synechococcus sp. and spinach PS II membranes have been investigated using low temperature near-IR spectroscopy and electron paramagnetic resonance (EPR) spectroscopy. We present evidence that two spectroscopically distinct redoxactive carotenoids are formed upon low-temperature illumination. The Car + near-IR absorption peak varies in wavelength and width as a function of illumination temperature. Also, the rate of decay during dark incubation of the Car + peak varies as a function of wavelength. Factor analysis indicates that there are two spectral forms of Car + (Car A + has an absorbance maximum of 982 nm, and Car B + has an absorbance maximum of 1027 nm) that decay at different rates. In Synechocystis PS II, we observe a shift of the Car + peak to shorter wavelength when oxidized tyrosine D (Y D •) is present in the sample that is explained by an electrostatic interaction between Y D • and a nearby-carotene that disfavors oxidation of Car B. The sequence of electron-transfer reactions in the secondary electron-transfer pathways of PS II is discussed in terms of a hole-hopping mechanism to attain the equilibrated state of the charge separation at low temperatures.

L'invention concerne un procede de production et d'isolement d'une diamine produite p... more L'invention concerne un procede de production et d'isolement d'une diamine produite par fermentation microbienne permettant de reduire a un minimum la formation de sels indesirables afin de fournir un procede moins couteux.

La presente invention concerne un organisme microbien non naturel (NNOMO) ayant une voie metaboli... more La presente invention concerne un organisme microbien non naturel (NNOMO) ayant une voie metabolique du methanol (MMP) qui peut ameliorer la disponibilite d'equivalents de reduction en presence de methanol. De tels equivalents de reduction peuvent etre utilises pour ameliorer le rendement de produit de composes organiques produits par l'organisme microbien, tels que le 3-hydroxyisobutyrate (3-HIB) ou l'acide methacrylique (MAA). La presente invention concerne egalement des procedes d'utilisation d'un tel organisme pour produire 3-HIB ou MAA.

Science Access, 2001

Under conditions when the primary electron-donation pathway from the O2-evolving complex in photo... more Under conditions when the primary electron-donation pathway from the O2-evolving complex in photosystem II (PSII) is inhibited, several alternate electron donors can be photooxidized. These include a monomeric chlorophyll (ChlZ), b-carotene (Car) and cytochrome b559. The involvement of these alternate electron donors and the redox role of a carotenoid in PSII are unique among photosynthetic reaction centers and stem from the very highly oxidizing intermediates that form in the process of water oxidation. ChlZ and Car photooxidation have been characterized by near-infrared absorbance, shifted-excitation Raman difference (SERDS) and EPR spectroscopies over a range of cryogenic temperatures from 30 to 120 K in both cyanobacterial PSII core complexes and spinach PSII membranes. The EPR signals of the individual species, previously not resolved at X-band frequency (9 GHz), are resolved at higher D-band frequency (130 GHz) in deuterated Synechococcus lividus PSII (Lakshmi, K.V., Reifler, ...

The Journal of Physical Chemistry B, 2009

β-carotene radicals produced in the hexagonal pores of the molecular sieve Cu(II)-MCM-41 were stu... more β-carotene radicals produced in the hexagonal pores of the molecular sieve Cu(II)-MCM-41 were studied by ENDOR and visible/near IR spectroscopies. ENDOR studies showed that neutral radicals of β-carotene were produced in humid air under ambient fluorescent light. The maximum absorption wavelengths of the neutral radicals were measured and were additionally predicted by using timedependent density functional theory (TD-DFT) calculations. An absorption peak at 750 nm, assigned to the neutral radical with a proton loss from the 4(4') position of the β-carotene radical cation in Cu (II)-MCM-41, was also observed in photosystem II (PS II) samples using near-IR spectroscopy after illumination at 20 K. This peak was previously unassigned in PS II samples. The intensity of the absorption peak at 750 nm relative to the absorption of chlorophyll radical cations and β-carotene radical cations increased with increasing pH of the PS II sample, providing further evidence that the absorption peak is due to the deprotonation of the β-carotene radical cation. Based on a consideration of possible proton acceptors that are adjacent to β-carotene molecules in photosystem II, as modeled in the X-ray crystal structure of Guskov et al. Nat. Struct. Mol. Biol. 2009, 16, 334-342, an electrontransfer pathway from a β-carotene molecule with an adjacent proton acceptor to P680 •+ is proposed.

Structure, 2004

Photosynthesis Research, 2008