Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.3.1.108 (TAT)
 2,389 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Most chloroplast proteins are synthesized in the cytosol and imported into chloroplasts. Many imported proteins are further targeted to the thylakoid membrane and lumen by the SEC1, TAT, or SRP/ALB3 translocases. Others are targeted to the inner chloroplast envelope membrane by undescribed translocases. Recently, a second SEC system (SEC2) consisting of SCY2, SECE2, and SECA2 was found in the chloroplast envelope. Null mutants of SCY2 in Arabidopsis (Arabidopsis thaliana) exhibit a severe embryo-lethal phenotype. To investigate the function of the SEC2 system in plants, we used inducible RNA interference to knock down SCY2 in Arabidopsis. Seedlings cultured with inducer were chlorotic with aberrant chloroplasts and undeveloped thylakoids, indicating an essential role for SCY2 in chloroplast biogenesis beyond embryo development. In SCY2 down-regulated seedlings, several thylakoid membrane proteins, including SCY1, ALB3, and TATC, and inner envelope membrane proteins, including TIC40, TIC110, and FTSH12, were reduced substantially, suggesting that they may be SEC2 substrates. Additional insight was achieved by the in vitro reconstitution of protein integration into chloroplast membranes. The results show that SCY1 and ALB3 target directly to the thylakoid membrane and are likely independent of SEC2. FTSH12 was integrated into the envelope membrane in a coupled import-integration reaction that was impaired by the SECA inhibitor sodium azide. The stromal intermediate of TIC40 integrated into the envelope in a reaction that was largely inhibited when antibodies against epitope-tagged SCY2 or SECE2 were applied. These data demonstrate that the SEC2 translocase likely integrates a subset of inner envelope membrane proteins, such as FTSH12 and TIC40.
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PMID:Identification of Putative Substrates of SEC2, a Chloroplast Inner Envelope Translocase. 2821 60

Chloroplast stromal factors involved in regulating thylakoid protein targeting are poorly understood. We previously reported that in Arabidopsis thaliana, the stromal localized chaperone HSP90C interacted with the nuclear-encoded thylakoid lumen protein PsbO1 and suggested a role for HSP90C in aiding PsbO1 thylakoid targeting. Using in organello transport assays, particularly with model substrates naturally expressed in stroma, in this study we showed that light or exogenous ATP, and HSP90C activity were required for Sec-dependent transport of GFP led by PsbO1 thylakoid targeting sequence. Using a previously identified PsbO1T200A mutant, we provided evidence that a stronger interaction between HSP90C and PsbO1 better facilitated its stroma-thylakoid trafficking. We also showed that SecY1, the channel protein of the thylakoid SEC translocase, specifically interacted with HSP90C in vivo. Inhibition of the chaperone ATPase activity suppressed the association of PsbO1GFP-HSP90C complex to SecY1. Together with analyzing the expression and accumulation of a few other thylakoid proteins that utilize the SRP, TAT or SEC translocation pathways, we propose a model in which HSP90C forms a guiding complex that interacts with thylakoid protein precursors and assists in their specific targeting to the thylakoid SEC translocon.
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PMID:Plastid chaperone HSP90C guides precursor proteins to the SEC translocase for thylakoid transport. 3285 83