Cloning and nucleotide sequence of a cDNA encoding a major fucoxanthin-, chlorophyll a/c-containing protein from the chrysophyte Isochrysis galbana: implications for evolution of the cab gene family.

We investigated the primary structure of a cDNA encoding a light-harvesting protein from the marine chrysophyte Isochrysis galbana. Antibodies raised against the major fucoxanthin, chlorophyll a/c-binding light-harvesting protein (FCP) of I. galbana were used to select a cDNA clone encoding one of the FCP apoproteins. The nucleic acid and deduced amino acid sequences reveal conserved regions within the first and third transmembrane spans with Chl a/b-binding proteins and with FCPs of another chromophyte. However, the amino acid identity between I. galbana FCP and other cab genes of FCPs is only ca. 30%. Phylogenetic analyses demonstrated that the FCP genes of both diatoms and chrysophytes sequenced to date are more closely related to cab genes encoding LHC I, CP 29, and CP 24 of higher plants than to cab genes encoding LHC II of chlorophytes. We propose that LHC I, CP 24 and CP 29 and FCP might have originated from a common ancestral chl binding protein and that the major LHC II of Chl a/b-containing organisms arose after the divergence between the chromophytes and the chlorophytes.