Abstract.A Laminaria saccharina genomic library in the phage EMBL 4 was used to isolate and sequence a full-length gene encoding a fucoxanthin-chlorophyll a/cbinding protein. Contrary to diatom homologues, the coding sequence is interrupted by an intron of about 900 bp which is located in the middle of the transit peptide. The deduced amino acid sequence of the mature protein is very similar to those of related proteins from Macrocystis pyrifera (Laminariales) and, to a lesser extent, to those from diatoms and Chrysophyceae. Seven of the eight putative chlorophyll-binding amino acids determined in green plants are also present.Alignments of different sequences related to the lightharvesting proteins (LHC) demonstrate a structural similarity among the three transmembrane helices and suggest a unique ancestral helix preceded by two [3-turns. The S-turns are conserved in front of the second helices of the chlorophyll a/c proteins more so than in chlorophyll a/b proteins.Phylogenetic trees generated from sequence data indicate that fucoxanthin-chlorophyll-binding proteins diverged prior to the separation of photosystem I and photosystem II LHC genes of green plants. Among the fucoxanthin-containing algae, LHC I or II families could not be distinguished at this time.

The main light‐harvesting fraction from Pelvetia canaliculata was isolated on a sucrose density gradient from digitonin‐solubilized chloroplasts. After further solubilization by dodecyl maltoside, the bulk fraction was separated into two subunits by preparative isoelectric focusing. The more acidic brown fraction was mainly composed of 22 kDa polypeptides having an apparent pI of 4.55. Its pigment composition was very simple, containing chlorophyll (Chi) a, Chi c and fucoxanthin. The in vivo spectral properties of fucoxanthin, namely a shift in light absorption to the green and efficient energy transmission to Chi a, were conserved in this subunit. No xanthophyll associated with photoprotection was found in this band, even when obtained from photoinhibited thalli. The less acidic green band contained predominantly 22 kDa polypeptides that were resolved into numerous components by denaturing isoelectric focusing. Its pigment composition was more complex, containing, in addition, pigments of the so‐called xanthophyll cycle. In photoinhibited thalli, about half of the violaxanthin was converted into antheraxanthin and zeaxanthin. All the pigments of the xanthophyll cycle were specifically associated with this subunit, and it may thus have a central role in the thermal dissipation of the absorbed light energy as postulated for light‐harvesting complex II isolated from green plants.

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The N-terminus of the major polypeptide component of the light-harvesting complex (LHC) from the brown alga Laminaria saccharina is blocked. Two partial sequences, one near the N-terminus and the other near the C-terminus, have been obtained by chemical cleavage with acetic acid and N-chlorosuccinimide. Four peptides were separated after trypsin digestion of the thylakoid membranes. One fragment is not phosphorylated, is not blocked, and has been sequenced. Purification on a reversed-phase column showed two forms of the LHC protein: the more hydrophobic form appears to be bound to photosystem I. These results are compared with LHC from other Chromophytes and the CAB family of green plants.

Accessory light-harvesting complexes (LHCFs) were isolated from the brown alga Laminaria saccharina. Complexes specifically associated with photosystem I or II are identical with each other with respect to molecular mass, isoelectric point and behavior on anion-exchange chromatography or non-denaturing isoelectric focusing. The purified complexes also have similar pigment composition and spectroscopic properties. It is concluded that LHC antennae associated with photosystem I or II cannot be distinguished biochemically. After screening of genomic and cDNA libraries produced from L. saccharina sporophytes, six lhcf genes were isolated. Sequence analysis of these lhcf genes showed a high level of homology between the encoded polypeptides. Comparisons with coding sequences of lhcf genes from Macrocystis pyrifera and expressed sequence tags from Laminaria digitata (two other Laminariales) indicated that these proteins are probably very similar in all brown algae. Another feature common to the lhcf genes characterized was the presence of an intron in the coding region corresponding to the plastid-targeting presequence. The sequence similarity extended to the 5 H and 3 H UTRs of several genes. In spite of the common origin of the chloroplasts, no light-regulating elements involved in the expression of the genes encoding the higher-plant light-harvesting proteins has been found in the UTRs.Keywords: fucoxanthin-chlorophyll c antenna; light-harvesting complex (LHC) gene family; pigment±protein complexes.Numerous studies (reviewed in [1]) have shown that the intrinsic chlorophyll a-binding light-harvesting complex (LHC) proteins from a wide variety of photosynthetic organisms share a homologous primary sequence and probably have a similar tertiary structure in the membranes. These proteins contain three distinct transmembrane helices, with the first and the third helix sharing distinct homology. It has been proposed that these proteins arose evolutionarily from a two-helix ancestral polypeptide. Gene duplication and fusion of the coding region resulted in a four-helix protein. The subsequent loss of the fourth helix resulted in the final three-helix form.Along with chlorophyll a, several additional types of chlorophyll are present. Specifically, higher plants contain chlorophyll b, and chromophytic algae have chlorophyll c. Carotenoids also play an important role in the LHCs. In chromophytic algae, particularly brown algae, fucoxanthin is the primary carotenoid. Sequence comparisons have also shown that several chlorophyll a-binding sites are conserved not only in LHCs from higher plants, but also in red algae and chromophytic algae. However, binding sites for carotenoids and accessory chlorophylls (such as chlorophyll c) are not clear. Data from CD and absorbance studies suggest that the organization of the pigment molecules in chlorophyll a/c antennae is different from the organization of chlorophyll a/b LHCs [2].Phylogenetic studies suggest that LHC polypeptides binding chlorophyll a/c diverged from the chlorophyll a/...