van 't Hof R, de Kruijff B
Department of Biochemistry of Membranes, Utrecht University, The Netherlands.
J Biol Chem. 1995 Sep 22;270(38):22368-73. doi: 10.1074/jbc.270.38.22368.
In order to get insight into the functioning of transit sequences in chloroplast protein transport, the import of the full-length transit peptide of ferredoxin (trfd) was investigated. trfd rapidly associated with chloroplasts under import conditions and becomes protected against externally added proteases. Import of radiolabeled trfd is inhibited equally efficiently by nonlabeled trfd as well as by the intact precursor of ferredoxin. This strongly suggests that trfd enters the general import pathway of proteins into chloroplasts. trfd import was stimulated by ATP, which is the first demonstration that ATP is involved in membrane translocation of a targeting signal. Imported trfd was membrane-associated but was also partially degraded by internal proteases, most likely present in the stroma, indicating that the membrane-associated fraction of trfd is en route to its functional localization. The degradation products are exported out of the organelle. In contrast to the import of the precursor of ferredoxin, the import of trfd was independent of protease-sensitive components on the chloroplast surface, indicating that the initial binding of precursor proteins may be facilitated by transit sequence-lipid interactions.
为了深入了解叶绿体蛋白质转运中转运序列的功能，对铁氧化还原蛋白全长转运肽（trfd）的导入进行了研究。在导入条件下，trfd迅速与叶绿体结合，并受到保护免受外部添加的蛋白酶的作用。放射性标记的trfd的导入同样有效地受到未标记的trfd以及铁氧化还原蛋白完整前体的抑制。这有力地表明trfd进入了蛋白质进入叶绿体的一般导入途径。trfd的导入受到ATP的刺激，这是首次证明ATP参与靶向信号的膜转运。导入的trfd与膜相关，但也被可能存在于基质中的内部蛋白酶部分降解，表明trfd与膜相关的部分正在前往其功能定位的途中。降解产物被输出到细胞器外。与铁氧化还原蛋白前体的导入不同，trfd的导入不依赖于叶绿体表面对蛋白酶敏感的成分，表明前体蛋白的初始结合可能通过转运序列-脂质相互作用而促进。
