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

Abstract

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. The AtFKBP13 protein is synthesized as a precursor that is imported into chloroplasts and processed to the mature form located in the thylakoid lumen, as shown by chloroplast import assays and Western blot analysis. Experiments show that AtFKBP13 is translocated across the thylakoid membrane by the ⌬pH-dependent pathway. Yeast twohybrid screening identified Rieske FeS protein, a subunit of the cytochrome bf complex in the photosynthetic electron transport chain, as an interacting partner for AtFKBP13. Both yeast two-hybrid and in vitro protein-protein interaction assays showed that the precursor, but not the mature form, of AtFKBP13 interacted with Rieske protein, suggesting that interaction between the two proteins occurs along the import pathway. When AtFKBP13 expression was suppressed by RNA interference method, the level of Rieske protein was significantly increased in the transgenic plants.

Immunophilins and Parvulins. Superfamily of Peptidyl Prolyl Isomerases in Arabidopsis

“…In this study, we retained the names of published FKBP members in plants. These include regular names such as AtFKBP12 Xu et al, 1998), AtFKBP15-1, AtFKBP15-2 (Luan et al, 1996), and AtFKBP13 (Gupta et al, 2002), and irregular names such as PAS1 and TWD1, which are named according to other circumstances such as phenotype of the mutants (Vittorioso et al, 1998;Kamphausen et al, 2002). For newly identified genes in this study, they were named after the calculated M r of mature proteins predicted from cDNA-deduced sequences.…”

“…The localization of AtFKBP13 was determined by both import and chloroplast fraction followed by western blot. It was also shown that AtFKBP13 was imported into thylakoid lumen through the DpH pathway (Gupta et al, 2002). Proteomics procedures designed to sequence all thylakoid lumen proteins uncovered several FKBPs including AtFKBP13,18,19,and 22 (Table I and references therein).…”

“…Disruption of AtFKBP42 gene function caused developmental defect (Kamphausen et al, 2002). A chloroplast FKBP has been shown to interact with a photosynthetic electron carrier and affects the accumulation of the protein (Gupta et al, 2002). As in animals, different members of immunophilins appear to play different roles in plants.…”

Introducing Immunophilins. From Organ Transplantation to Plant Biology

“…With relevance to chloroplast immunophilins, Romano and coworkers further studied the Arabidopsis cyclophilin AtCYP20-2 and show that this cyclophilin may associate with the periphery of PSII supercomplexes (Romano et al, 2004b). Together with earlier reports (Fulgosi et al, 1998;Gupta et al, 2002), these studies suggest that a subset of immunophilins may have specifically evolved to fulfill functions that are unique to photosynthetic organisms. Towards the functional significance of immunophilins in developmental processes, Vespa et al (2004) show that FIP37, an interacting partner for AtFKBP12, is involved in cell division control.…”

“…isoforms (Gupta et al, 2002;Peltier et al, 2002;Schubert et al, 2002). Whilst two of the lumenal immunophilins have been shown to be functionally associated with photosynthetic complex components (Fulgosi et al, 1998;Gupta et al, 2002), the specific function of the majority of chloroplast isoforms remains to be elucidated.…”