Koll H, Guiard B, Rassow J, Ostermann J, Horwich A L, Neupert W, Hartl F U
Institut für Physiologische Chemie, München, Germany.
Cell. 1992 Mar 20;68(6):1163-75. doi: 10.1016/0092-8674(92)90086-r.
Cytochrome b2 reaches the intermembrane space of mitochondria by transport into the matrix followed by export across the inner membrane. While in the matrix, the protein interacts with hsp60, which arrests its folding prior to export. The bacterial-type export sequence in pre-cytochrome b2 functions by inhibiting the ATP-dependent release of the protein from hsp60. Release for export apparently requires, in addition to ATP, the interaction of the signal sequence with a component of the export machinery in the inner membrane. Export can occur before import is complete provided that a critical length of the polypeptide chain has been translocated into the matrix. Thus, hsp60 combines two activities: catalysis of folding of proteins destined for the matrix, and maintaining proteins in an unfolded state to facilitate their channeling between the machineries for import and export across the inner membrane. Anti-folding signals such as the hydrophobic export sequence in cytochrome b2 may act as switches between these two activities.
细胞色素b2通过先转运至线粒体基质再穿过内膜输出的方式到达线粒体内膜间隙。在基质中时，该蛋白质与hsp60相互作用，hsp60会在其输出前阻止其折叠。细胞色素b2前体中的细菌型输出序列通过抑制蛋白质从hsp60的ATP依赖性释放发挥作用。除了ATP外，输出释放显然还需要信号序列与内膜中输出机制的一个组分相互作用。只要多肽链的关键长度已转运至基质中，在导入完成之前就可以发生输出。因此，hsp60兼具两种活性：催化运往基质的蛋白质的折叠，以及使蛋白质保持未折叠状态以促进其在内膜的导入和输出机制之间的通道运输。抗折叠信号，如细胞色素b2中的疏水输出序列，可能充当这两种活性之间的开关。
