A chlorophyll a/b-binding protein homolog that is induced by iron deficiency is associated with enlarged photosystem I units in the eucaryotic alga Dunaliella salina.
Adaptation of the halotolerant alga Dunaliella salina to iron deprivation involves extensive changes of chloroplast morphology, photosynthetic activities, and induction of a major 45-kDa chloroplast protein termed Tidi. Partial amino acid sequencing of proteolytic peptides suggested that Tidi resembles chlorophyll a/b-binding proteins which compose light-harvesting antenna complexes (LHC) (Varsano, T., Kaftan, D., and Pick, U. (2003) J. Plant Nutr. 26, 2197-2210). Here we show that Tidi shares the highest amino acid sequence similarity with light-harvesting I chlorophyll a/b-binding proteins from higher plants but has an extended proline-rich N-terminal domain. The accumulation of Tidi is reversed by iron supplementation, and its level is inversely correlated with photosystem I (PS-I) reaction center proteins. In native gel electrophoresis, Tidi co-migrates with enlarged PS-I-LHC-I super-complexes. Single particle electron microscopy analysis revealed that PS-I units from iron-deficient cells are larger (31 and 37 nm in diameter) than PS-I units from control cells (22 nm). The 77 K chlorophyll fluorescence emission spectra of isolated complexes suggest that the Tidi-LHC-I antenna are functionally coupled to the reaction centers of PS-I. These findings indicate that Tidi acts as an accessory antenna of PS-I. The enlargement of PS-I antenna in algae and in cyanobacteria under iron deprivation suggests a common limitation that requires rebalancing of the energy distribution between the two photosystems.
Varsano
Tal
T
Department of Biological Chemistry and Electron Microscopy Unit, Weizmann Institute of Science, Rehovot 76100, Israel.
Wolf
Sharon G
SG
Pick
Uri
U
D000595:Amino Acid Sequence; D015152:Blotting, Northern; D002734:Chlorophyll / Q000737:chemistry*; D000077194:Chlorophyll A; D003001:Cloning, Molecular; D000458:Cyanobacteria / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D056890:Eukaryota / Q000378:metabolism*; D007150:Immunohistochemistry; D007501:Iron / Q000737:chemistry / Q000378:metabolism; D000090463:Iron Deficiencies; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D045331:Photosystem I Protein Complex / Q000737:chemistry* / Q000378:metabolism; D011392:Proline / Q000737:chemistry; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry; D012333:RNA, Messenger / Q000378:metabolism; D020539:Sequence Analysis, Protein; D017386:Sequence Homology, Amino Acid; D013050:Spectrometry, Fluorescence; D013696:Temperature; D020524:Thylakoids / Q000378:metabolism; D013997:Time Factors; D014158:Transcription, Genetic
D045342:Light-Harvesting Protein Complexes; D045331:Photosystem I Protein Complex; D011506:Proteins; D012333:RNA, Messenger; D002734:Chlorophyll; C037184:chlorophyll b; D011392:Proline; D007501:Iron; D000077194:Chlorophyll A