David W. Krogmann

The Crystal Structure of a Cyanobacterial Water-Soluble Carotenoid Binding Protein

Carotenoids undergo a wide range of photochemical reactions in animal, plant, and microbial systems. In photosynthetic organisms, in addition to light harvesting, they perform an essential role in protecting against light-induced damage by quenching singlet oxygen, superoxide anion radicals, or triplet-state chlorophyll. We have determined the crystal structure of a water-soluble orange carotenoid protein (OCP) isolated from the cyanobacterium Arthrospira maxima at a resolution of 2.1 A. OCP forms a homodimer with one carotenoid molecule per monomer. The carotenoid binding site is lined by a striking number of methionine residues. The structure reveals several possible ways in which the protein environment influences the spectral properties of the pigment and provides insight into how the OCP carries out its putative functions in photoprotection.

Electron donors to P700 in cyanobacteria and algae: An instance of unusual genetic variability

Abstract Cytochrome c -553 and/or plastocyanin have been isolated from many cyanobacteria and several eukaryotic algae. The isoelectric point for both the cytochrome and plastocyanin varies from that of a basic protein (p I 9.3) in the filamentous cyanobacteria to that of an acidic protein (p I 3.8) in unicellular cyanobacteria and eukaryotes. The cytochrome from a given genus may show isomeric forms distinguishable in either net charge or nonpolar character. Some of the variation in net charge between the cytochromes from different genera is localized in one region of the primary structure.

A carotenoid-protein from cyanobacteria

Abstract Easily solubilized carotenoid-containing proteins have been found in aqueous extracts from three genera of cyanobacteria. The three proteins have been purified, and the absorption spectra have been determined to be virtually identical with absorption maxima at 495 and 465 nm. During the purification the orange protein spontaneously changed to a red protein with a single, broad absorption maximum at 505 nm. The orange protein showed a molecular weight of 47 000 on gel filtration while that of the red protein was 26 700. Sodium dodecyl sulfate polacrylamide gel electrophoresis indicated a single polypeptide of M r 16 000 in both the red and orange forms, but this method removed the chromophore from the proteins. The main carotenoid component of the complex was determined to be 3′-hydroxy-4-keto-ββ-carotenoid or 3′-hydroxyechinenone. The number of carotenoid molecules per molecule of orange protein of molecular weight 47 000 was between 20 and 40. The stoichiometry of carotenoid to protein seemed reasonably constant.

Isolation of photosynthetic catalysts from cyanobacteria

Methods are described for the isolation of ferredoxins I and II, cytochrome c-553, cytochrome f, cytochrome c-550 and plastocyanin from large quantities of various cyanobacteria. The amino acid composition of cytochrome c-550 is reported. There is a variation in the relative amounts of these proteins in different batches of cells which may relate to the nutritional status of the organisms.

Discoveries in Oxygenic Photosynthesis (1727–2003): A Perspective

We present historic discoveries and important observations, related to oxygenic photosynthesis, from 1727 to 2003. The decision to include certain discoveries while omitting others has been difficult. We are aware that ours is an incomplete timeline. In part, this is because the function of this list is to complement, not duplicate, the listing of discoveries in the other papers in these history issues of Photosynthesis Research. In addition, no one can know everything that is in the extensive literature in the field. Furthermore, any judgement about significance presupposes a point of view. This history begins with the observation of the English clergyman Stephen Hales (1677–1761) that plants derive nourishment from the air; it includes the definitive experiments in the 1960–1965 period establishing the two-photosystem and two-light reaction scheme of oxygenic photosynthesis; and includes the near-atomic resolution of the structures of the reaction centers of these two Photosystems, I and II, obtained in 2001–2002 by a team in Berlin, Germany, coordinated by Horst Witt and Wolfgang Saenger. Readers are directed to historical papers in Govindjee and Gest [(2002a) Photosynth Res 73: 1–308], in Govindjee, J. Thomas Beatty and Howard Gest [(2003a) Photosynth Res 76: 1–462], and to other papers in this issue for a more complete picture. Several photographs are provided here. Their selection is based partly on their availability to the authors (see Figures 1–15). Readers may view other photographs in Part 1 (Volume 73, Photosynth Res, 2002), Part 2 (Volume 76, Photosynth Res, 2003) and Part 3 (Volume 80 Photosynth Res, 2004) of the history issues of Photosynthesis Research. Photographs of most of the Nobel-laureates are included in Govindjee, Thomas Beatty and John Allen, this issue. For a complementary time line of anoxygenic photosynthesis, see H. Gest and R. Blankenship (this issue).

Large scale preparation of pure phycobiliproteins

This paper describes simple procedures for the purification of large amounts of phycocyanin and allophycocyanin from the cyanobacterium Microcystis aeruginosa. A homogeneous natural bloom of this organism provided hundreds of kilograms of cells. Large samples of cells were broken by freezing and thawing. Repeated extraction of the broken cells with distilled water released phycocyanin first, then allophycocyanin, and provides supporting evidence for the current models of phycobilisome structure. The very low ionic strength of the aqueous extracts allowed allophycocyanin release in a particulate form so that this protein could be easily concentrated by centrifugation. Other proteins in the extract were enriched and concentrated by large scale membrane filtration. The biliproteins were purified to homogeneity by chromatography on DEAE cellulose. Purity was established by HPLC and by N-terminal amino acid sequence analysis. The proteins were examined for stability at various pHs and exposures to visible light.

Soluble Electron Transfer Catalysts of Cyanobacteria

This review covers only a fraction of the area of one written a dozen years ago on photosynthesis in cyanobacteria (Ho and Krogmann, 1982) yet it cites many more references than that earlier work. The power of reductionist laboratory science has increased immensely in the intervening years. The soluble electron transfer catalysts of photosynthesis have received disproportionate attention since soluble proteins are more easily dealt with by the techniques of protein chemistry. Research on each of the catalysts reviewed here has exposed a variety of insights through the tools of contemporary science. The many studies of different forms of ferredoxin in cyanobacteria promise new understanding of the regulation of electron transfer and its mechanism. The crystal structures of ferredoxin, ferredoxin-NADP+ oxidoreductase, flavodoxin and plastocyanin are elegant examples of what our broader understanding will become. The powerful technique of gene deletion used on cytochrome c 6 (cytochrome c 553) has done more than confirm preconceptions. It has given us the intriguing puzzle of why more than two routes of electron flow between carriers of very similar redox potential may be used. The low potential cytochrome c beckons for an explanation of its catalytic function and for an understanding of its role in the ancient origin of other cytochromes. Finally, hydrogenase, whose catalytic act is the simplest—the movement of an electron to or from a proton—seems ready for understanding. Hydrogenase has a long history of fragility and activity loss during purification. One type of hydrogenase has now been purified and there are glimpses of its metabolic role.

Studies of the multiple forms of ferredoxin-NADP oxidoreductase from spinach☆

Abstract Six different forms of ferredoxin-NADP Oxidoreductase from spinach were separated by isoelectric focusing and were found to differ in their specific activities in various assay systems and in their affinity for NADPH. The forms of the enzyme were found to be interconvertible when the enzyme was stored in the cold.

Plastocyanin participation in chloroplast Photosystem I

Abstract French pressure cell disruption of spinach chloroplasts releases much of the plastocyanin from chloroplast membranes. Heavy particles obtained from French pressure cell disrupted chloroplasts lose most of their plastocyanin while light particles retain a high plastocyanin to chlorophyll ratio. Photosystem I activity is dependent on the presence of plastocyanin in our preparations.

A light-dependent oxygen-reducing system from Anabaena variabilis

Abstract Photosynthetic lamellae from Anabaena variabilis catalyze a vigorous photoreduction of O2 to H2O2. The electrons come to O2 from an artificial donor, reduced 2,3′,6-trichlorophenolindophenol, and the reaction does not require an exogenous autoxidizable substance. Evidence is presented to show that reduced 2,3′,6-trichlorophenolindophenol can donate electrons at two distinct sites. Photoreduction of O2 is inhibited by antibodies which block the function of the ferredoxin-reducing substance. The O2-reducing system may result from the formation of a reduced photoproduct which is more accessible to autoxidation than is the analogous product formed in higher plant chloroplasts.