The 15-kDa forms of the apo-peridinin-chlorophyll a protein (PCP) in dinoflagellates show high identity with the apo-32 kDa PCP forms, and have similar N-terminal leaders and gene arrangements.

Full-length genomic sequences encoding apo peridinin-chlorophyll a proteins (PCPs) from Heterocapsa pygmaea have been obtained by PCR. Two of the derived mature proteins of 150 residues have molecular masses of 15,795 and 15,780, respectively. Contrary to an earlier report, these show a high degree of identity (approximately 70%) over the whole of both domains to the mature 32-kDa PCP forms. The two genes lack introns, are arranged in tandem and separated by 526 bp. A putative N-terminal extension with three domains characteristic of a signal sequence, a chloroplast-targeting sequence and a thylakoid lumen-directing sequence, is present. Modelling of the Heterocapsa PCP amino acid sequence on to the high-resolution structure available for Amphidinium PCP shows that the main differences between two forms are in trimer contact regions.

Crystal structure of a phycourobilin-containing phycoerythrin at 1.90-A resolution.

The structure of R-phycoerythrin (R-PE) from the red alga Griffithsia monilis was solved at 1.90-A resolution by molecular replacement, using the atomic coordinates of cyanobacterial phycocyanin from Fremyella diplosiphon as a model. The crystallographic R factor for the final model is 17.5% (Rfree 22.7%) for reflections in the range 100-1.90 A. The model consists of an (alphabeta)2 dimer with an internal noncrystallographic dyad and a fragment of the gamma-polypeptide. The alpha-polypeptide (164 amino acid residues) has two covalently bound phycoerythrobilins at positions alpha82 and alpha139. The beta-polypeptide (177 residues) has two phycoerythrobilins bound to residues beta82 and beta158 and one phycourobilin covalently attached to rings A and D at residues beta50 and beta61, respectively. The electron density of the gamma-polypeptide is mostly averaged out by threefold crystallographic symmetry, but a dipeptide (Gly-Tyr) and one single Tyr could be modeled. These two tyrosine residues of the gamma-polypeptide are in close proximity to the phycoerythrobilins at position beta82 of two symmetry-related beta-polypeptides and are related by the same noncrystallographic dyad as the (alphabeta)2 dimer. Possible energy transfer pathways are discussed briefly.

Independent evolution of the prochlorophyte and green plant chlorophyll a/b light-harvesting proteins.

The prochlorophytes are oxygenic prokaryotes differing from other cyanobacteria by the presence of a light-harvesting system containing both chlorophylls (Chls) a and b and by the absence of phycobilins. We demonstrate here that the Chl a/b binding proteins from all three known prochlorophyte genera are closely related to IsiA, a cyanobacterial Chl a-binding protein induced by iron starvation, and to CP43, a constitutively expressed Chl a antenna protein of photosystem II. The prochlorophyte Chl a/b protein (pcb) genes do not belong to the extended gene family encoding eukaryotic Chl a/b and Chl a/c light-harvesting proteins. Although higher plants and prochlorophytes share common pigment complements, their light-harvesting systems have evolved independently.

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.

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 alpha-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 Phaeodactylum and 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 approximately 17% sucrose and the decylmaltoside LHC one at approximately 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 degrees 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.

Amino acid sequence of the beta-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.