A cyclophilin links redox and light signals to cysteine biosynthesis and stress responses in chloroplasts.

Cyclophilins belong to a large family of enzymes called "peptidyl prolyl isomerases" that assist protein folding and assembly. The cyclophilin CYP20-3 (also known as "ROC4") is the only member of this group located in the stroma (soluble phase) of chloroplasts. In the present study we isolated mutant Arabidopsis plants defective in the CYP20-3 gene and found them to be hypersensitive to oxidative stress conditions created by high light levels, rose bengal, high salt levels, and osmotic shock.

A chloroplast cyclophilin functions in the assembly and maintenance of photosystem II in Arabidopsis thaliana.

Photosynthetic light reactions rely on the proper function of large protein complexes (including photosystems I and II) that reside in the thylakoid membrane. Although their composition, structure, and function are known, the repertoire of assembly and maintenance factors is still being determined. Here we show that an immunophilin of the cyclophilin type, CYP38, plays a critical role in the assembly and maintenance of photosystem II (PSII) supercomplexes (SCs) in Arabidopsis.

A WD40 domain cyclophilin interacts with histone H3 and functions in gene repression and organogenesis in Arabidopsis.

Chromatin-based silencing provides a crucial mechanism for the regulation of gene expression. We have identified a WD40 domain cyclophilin, CYCLOPHILIN71 (CYP71), which functions in gene repression and organogenesis in Arabidopsis thaliana. Disruption of CYP71 resulted in ectopic activation of homeotic genes that regulate meristem development.

Structural comparison of oxidized and reduced FKBP13 from Arabidopsis thaliana.

AtFKBP13, an immunophilin in the chloroplast thylakoid lumen, participates in redox-regulatory processes via a pair of conserved disulfide bonds that are present at the N- and C-termini of the protein. Characterization of this protein by structural and biochemical analysis has revealed a novel mechanism of redox regulation in the thylakoid lumen. The protein is active in its oxidized form but is inactivated after reduction by the thioredoxin system.

Expression, purification, crystallization and preliminary X-ray diffraction analysis of Arabidopsis thaliana cyclophilin 38 (AtCyp38).

AtCyp38 is one of the highly divergent multidomain cyclophilins from Arabidopsis thaliana. A recombinant form of AtCyp38 (residues 83-437) was expressed in Escherichia coli and purified to homogeneity. The protein was crystallized using the vapour-batch technique with PEG 6000 and t-butanol as precipitants.

Structural analysis uncovers a role for redox in regulating FKBP13, an immunophilin of the chloroplast thylakoid lumen.

Change in redox status has long been known to link light to the posttranslational regulation of chloroplast enzymes. So far, studies have been conducted primarily with thioredoxin-linked members of the stroma that function in a broad array of biosynthetic and degradatory processes. Consequently, little is known about the role of redox in regulating the growing number of enzymes found to occur in the lumen, the site of oxygen evolution in thylakoid membranes.

Immunophilins and parvulins. Superfamily of peptidyl prolyl isomerases in Arabidopsis.

Immunophilins are defined as receptors for immunosuppressive drugs including cyclosporin A, FK506, and rapamycin. The cyclosporin A receptors are referred to as cyclophilins (CYPs) and FK506- and rapamycin-binding proteins are abbreviated as FKBPs. These two groups of proteins (collectively called immunophilins) share little sequence homology, but both have peptidyl prolyl cis/trans isomerase (PPIase) activity that is involved in protein folding processes.

A chloroplast FKBP interacts with and affects the accumulation of Rieske subunit of cytochrome bf complex.

Immunophilins are intracellular receptors of the immunosuppressants cyclosporin A, FK506, and rapamycin. Although all immunophilins possess peptidyl-prolyl isomerase activity and are identified from a wide range of organisms, little is known about their cellular functions. We report the characterization and functional analysis of an FK506 and rapamycin-binding protein (AtFKBP13) from Arabidopsis.

Functional relationship of cytochrome c(6) and plastocyanin in Arabidopsis.

Photosynthetic electron carriers are important in converting light energy into chemical energy in green plants. Although protein components in the electron transport chain are largely conserved among plants, algae and prokaryotes, there is thought to be a major difference concerning a soluble protein in the thylakoid lumen. In cyanobacteria and eukaryotic algae, both plastocyanin and cytochrome c(6) mediate electron transfer from cytochrome b(6)f complex to photosystem I.

Functional cloning and characterization of a plant efflux carrier for multidrug and heavy metal detoxification.

We have identified a detoxifying efflux carrier from Arabidopsis using a functional cloning strategy. A bacterial mutant, KAM3, is deficient in multidrug resistance and does not survive on medium containing norfloxacin. After transformation of KAM3 cells with an Arabidopsis cDNA library, transformants were selected for restored growth on the toxic medium.