Küchler Michael, Decker Susanne, Hörmann Friederike, Soll Jürgen, Heins Lisa
Botanisches Institut, Department Biologie I, Universität München, Menziger Strasse 67, D-80638 München, Germany.
EMBO J. 2002 Nov 15;21(22):6136-45. doi: 10.1093/emboj/cdf621.
Pre-protein translocation into chloroplasts is accomplished by two distinct translocation machineries in the outer and inner envelope, respectively. We have isolated the translocon at the inner envelope membrane (Tic complex) by blue-native PAGE and describe a new Tic subunit, Tic62. Tic62, together with Tic110 and Tic55, forms a core translocation unit. The N-terminus of Tic62 shows strong homologies to NAD(H) dehydrogenases in eukaryotes and to Ycf39-like proteins present in cyanobacteria and non-green algae. The stromal-facing C-terminus of Tic62 contains a novel, repetitive module that interacts with a ferredoxin-NAD(P)(+) oxidoreductase. Ferredoxin-NAD(P)(+) oxidoreductase catalyses the final electron transfer of oxygenic photosynthesis from ferredoxin to NAD(P). Substrates that interfere with either NAD binding, such as deamino-NAD, or influence the ratio of NAD(P)/NAD(P)H, such as ruthenium hexamine trichloride, modulate the import characteristics of leaf-specific ferredoxin-NAD(P)(+) oxidoreductase isologues differently. We conclude that the Tic complex can regulate protein import into chloroplasts by sensing and reacting to the redox state of the organelle.
前体蛋白分别通过外膜和内膜中两种不同的转运机制转运到叶绿体中。我们通过蓝色非变性聚丙烯酰胺凝胶电泳分离出了内膜转位子（Tic复合物），并描述了一种新的Tic亚基Tic62。Tic62与Tic110和Tic55一起形成了一个核心转运单元。Tic62的N端与真核生物中的NAD(H)脱氢酶以及蓝细菌和非绿藻中存在的Ycf39样蛋白具有很强的同源性。Tic62面向基质的C端包含一个新的重复模块，该模块与铁氧化还原蛋白-NAD(P)(+)氧化还原酶相互作用。铁氧化还原蛋白-NAD(P)(+)氧化还原酶催化有氧光合作用中从铁氧化还原蛋白到NAD(P)的最终电子转移。干扰NAD结合的底物，如脱氨基-NAD，或影响NAD(P)/NAD(P)H比例的底物，如三氯化六氨合钌，对叶特异性铁氧化还原蛋白-NAD(P)(+)氧化还原酶同工型的导入特性有不同的调节作用。我们得出结论，Tic复合物可以通过感知细胞器的氧化还原状态并做出反应来调节蛋白向叶绿体中的导入。
