Pamela M. Wrench

Structural Basis of Light Harvesting by Carotenoids: Peridinin-Chlorophyll-Protein from Amphidinium carterae

Peridinin-chlorophyll-protein, a water-soluble light-harvesting complex that has a blue-green absorbing carotenoid as its main pigment, is present in most photosynthetic dinoflagellates. Its high-resolution (2.0 angstrom) x-ray structure reveals a noncrystallographic trimer in which each polypeptide contains an unusual jellyroll fold of the α-helical amino- and carboxyl-terminal domains. These domains constitute a scaffold with pseudo-twofold symmetry surrounding a hydrophobic cavity filled by two lipid, eight peridinin, and two chlorophyll a molecules. The structural basis for efficient excitonic energy transfer from peridinin to chlorophyll is found in the clustering of peridinins around the chlorophylls at van der Waals distances.

The light‐harvesting chlorophyll a‐c‐binding protein of dinoflagellates: a putative polyprotein

The principle light‐harvesting chlorophyll a‐c‐binding protein of Amphidinium carterae of 19 kDa is encoded as a polyprotein translated from a 6.1 kb mRNA. The cDNA sequences indicate that each derived polypeptide is contiguous with the next and that the mature peptides are formed by cleavage at a C‐terminal arginine residue. Comparison of the amino‐acid sequences shows the Amphidinium protein to be most closely related to the fucoxanthin‐chlorophyll‐protein (Fcp) of Phaeodactylumand less related to the chlorophyll a‐b‐binding (Cab) proteins including those from Euglena.

The major intrinsic light-harvesting protein of Amphidinium : characterization and relation to other light-harvesting proteins

A major light‐harvesting complex (LHC) has been obtained from thylakoids of Amphidinium carterae solubilized with digitonin or decylmaltoside and separated by sucrose‐gradient centrifugation. The digitonin‐LHC forms a dark brown band at ‐17% sucrose and the decylmaltoside LHC one at ‐7% sucrose. Excellent energy transfer is retained from chlorophyll c and carotenoid to chlorophyll a. Absorbance and fluorescence excitation spectra show the existence of two major forms of chlorophyll c, one absorbing at 634 nm and the other at 649 nm. Linear dichroism spectra show the Qy transition of both forms of chlorophyll c to be aligned at <35° to the membrane plane. On sodium dodecylsulfate polyacrylamide gels the complex resolves as a single band of 19 kDa. A partial amino acid sequence shows the N‐terminus to be unblocked but modified; there is a persistent ambiguity of Ser/Asn at residue 4 and evidence for multiple but very similar polypeptides within the 19 kDa band. The peptide has strong identity with the N‐terminal regions of LHC from Phaeodactylum and Pavlova and LHC 1 of higher plants. Antibodies to the 19 kDa peptide react weakly with LHC of brown algae, diatoms and Prymnesiophytes but not with those of higher plants or Cryptophytes.

Two distinct forms of the peridinin-chlorophyll a-protein from Amphidinium carterae☆

Peridinin-chlorophyll a-proteins (PCPs) have been purified by combination of ammonium sulphate precipitation and cation exchange chromatography. The amino acid sequences of several of the most abundant forms have been deduced by direct protein sequencing and from DNA and indicate a highly conserved multi-gene family. At least two of the PCP genes are tandemly arranged. A novel form of the protein was also obtained in low yield with fewer peridinins (six vs eight) per chlorophyll a and with a different molecular mass (34 kDa vs 32 kDa) of its apoprotein. It had only 31% sequence identity with any of the more abundant PCP forms but retained a two-domain structure.

Chlorophyll proteins of the prymnesiophyte Pavlova lutherii (Droop) comb. nov.: Identification of the major light-harvesting complex

Abstract A chlorophyll ac-fucoxanthin light-harvesting protein has been separated by SDS-polyacrylamide gel electrophoresis and by digitonin-sucrose density centrifigation from thylakoids of Pavlova lutherii. It contains a single major polypeptide of 21 kDa, comprises 69% of the total chlorophyll a and is enriched in chlorophyll c compared to the thylakoids. Energy transfer from chlorophyll c and fucoxanthin to chlorophyll a was demonstrated within the protein complex. Antibodies to the 21 kDa apoprotein showed cross-reactivity with the 26–28 kDa apoproteins of higher plant light-harvesting chlorophyll a b protein and with the 19 kDa apoprotein of the light-harvesting complex of diatoms, but much reduced or no cross-reactivity with the major thylakoid polypeptides of dinoflagellates and cryptophytes.

Changes in plastid proteins during ripening of tomato fruits

Summary Plastids and plastid fragments were recovered from homogenates of the pericarp tissue of mature-green and ripening tomato fruits by differential centrifugation followed by sucrose density gradient centrifugation. The fractions were defined by their positions in the gradient, by their chlorophyll, carotenoid and protein contents, and by the spectra of membrane proteins revealed by polyacrylamide gel electrophoresis. The light harvesting complex and photosystem proteins and the ±- and ²-subunits of coupling factor (CFI) were identified by immunological methods. The proteins of the light harvesting complex and the photosystems were the major membrane proteins in the chloroplasts recovered from mature-green fruit but were less prominent in the plastids from pink fruit and absent in the chromoplasts or ripe fruit. By contrast, the coupling factor subunits were prominent in the membrane of chloroplasts and chromoplasts. The proteins most prominent in chromoplast membranes were also detected in chloroplast fragments, which were less dense than the whole chloroplasts, and which lacked the photosystem proteins. Chloroplast membrane proteins represented about 12 per cent of the protein in mature-green tissue; about 8 per cent of the protein of ripe fruit was recovered as chromoplast membrane protein. Ribulose bisphosphate carboxylase decreased through ripening but even in the maturegreen tissue it represented only 0.3 per cent of total protein indicating that fruit chloroplasts have a very high ratio of photosystem protein to ribulose bisphosphate carboxylase relative to leaf chloroplasts.

Amino acid sequence of the β-subunit of phycoerythrin from the cryptophyte algae Chroomonas CS 24

The full amino acid sequence of the beta-subunit of Chroomonas CS24 phycoerythrin has been determined by conventional Edman degradation and mass spectrometry. The sequence compromises 177 amino acids with a molecular mass of 18669 Da. It is 91.5% identical to the deduced amino acid sequence of Cryptomonas phi beta-phycoerythrin (Reith, M. and Douglas, S. (1990) Plant Mol. Biology 15, 585-592). The chromophores are bound by single thioether linkages. No evidence of microheterogeneity was found confirming that both beta-subunits of the holoprotein are identical.

A Complex Gene Encoding a Dinoflagellate Light-Harvesting Protein

Most of the chlorophyll in eukaryotic organisms is bound to intrinsic light-harvesting complexes. Although these complexes have apoproteins of widely differing Mr (17–30kDa) and bind almost the entire range of photosynthetic pigments, they are evolutionarily related [1]. In the model proposed for Pea LHCII [2] the chlorophylls are bound to the transmembrane helices and sequence alignments suggest putative chlorophyll-binding residues are conserved among even distantly related LHCs [1,3–6]. Another common feature is that LHC proteins are encoded by multigene nuclear families, although the roles of the different members are not clear. In two groups of algae, Euglenoids [7] and Dinoflagellates [8], multiple LHC genes have become fused and encode large polyproteins, which are cleaved after transfer to the chloroplast. We report here approximately 3kb of the sequence of an LHC gene from Amphidinium including the 5’ end. The pattern of introns supports a differential splicing explanation for the dramatic size variation (6kb reducing to 3kb) of LHC mRNA when algae are grown at low or intermediate light intensities [9].