title: Photosystem II damage and repair cycle in the green alga Dunaliella salina: involvement of a chloroplast-localized HSP70.
abstract: The involvement of HSP70B in the photosystem II damage and repair process in Dunaliella salina was investigated. A full-length cDNA of the D. salina hsp70B gene was cloned and sequenced. Expression patterns of the hsp70B gene were investigated upon shifting a D. salina culture from low-light to high-light growth conditions, designed to significantly accelerate the rate of PSII photodamage. Northern blot analyses and nuclear run-on transcription assays revealed a significant but transient induction of hsp70B gene transcription, followed by a subsequent increase in HSP70B protein synthesis and accumulation. Mild detergent solubilization of photoinhibited thylakoid membranes, in which photodamaged PSII centers had accumulated, followed by native gel electrophoresis revealed the formation of a 320 kDa protein complex that contained, in addition to the HSP70B, the photodamaged but as yet undegraded D1 protein as well as D2 and CP47. Evidence suggested that the 320 kDa complex is a transiently forming PSII repair intermediate. Denaturing solubilization of the 320 kDa PSII repair intermediate by SDS-urea resulted in cross-linking of its polypeptide constituents, yielding a 160 kDa protein complex. The role of the HSP70B in the repair of photodamaged PSII centers, e.g. in stabilizing the disassembled PSII-core complex and in facilitating the D1 degradation and replacement process, is discussed.
authors.affiliation: Department of Plant and Microbial Biology, 111 Koshland Hall, University of California, Berkeley, CA 94720-3102, USA.
authors.forename: K
authors.initials: K
authors.lastname: Yokthongwattana
authors.forename: B
authors.initials: B
authors.lastname: Chrost
authors.forename: S
authors.initials: S
authors.lastname: Behrman
authors.forename: C
authors.initials: C
authors.lastname: Casper-Lindley
authors.forename: A
authors.initials: A
authors.lastname: Melis
mesh_terms: D000595:Amino Acid Sequence; D000460:Chlorophyta / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D003001:Cloning, Molecular; D005786:Gene Expression Regulation / Q000528:radiation effects; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects; D008027:Light; D008969:Molecular Sequence Data; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D045332:Photosystem II Protein Complex; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D020524:Thylakoids / Q000378:metabolism / Q000528:radiation effects
chemical_list: D018840:HSP70 Heat-Shock Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex