Chauwin J F, Oster G, Glick B S
Department of Molecular and Cellular Biology, University of California, Berkeley 94720-3112, USA.
Biophys J. 1998 Apr;74(4):1732-43. doi: 10.1016/S0006-3495(98)77884-1.
Mitochondrial precursor proteins are imported from the cytosol into the matrix compartment through a proteinaceous translocation pore. Import is driven by mitochondrial Hsp70 (mHsp70), a matrix-localized ATPase. There are currently two postulated mechanisms for this function of mHsp70: 1) The "Brownian ratchet" model proposes that the precursor chain diffuses within the pore, and that binding of mHsp70 to the lumenal portion of the chain biases this diffusion. 2) The "power stroke" model proposes that mHsp70 undergoes a conformational change that actively pulls the precursor chain through the pore. Here we formulate these two models quantitatively, and compare their performance in light of recent experimental evidence that precursor chains interact strongly with the walls of the translocation pore. Under these conditions the simulated Brownian ratchet is inefficient, whereas the power stroke mechanism seems to be a plausible description of the import process.
线粒体前体蛋白通过蛋白质转运孔从细胞质溶胶导入基质区室。导入过程由线粒体Hsp70（mHsp70，一种定位于基质的ATP酶）驱动。目前关于mHsp70的这一功能有两种假说机制：1）“布朗棘轮”模型提出前体链在孔内扩散，并且mHsp70与链的腔内部位结合会使这种扩散产生偏差。2）“动力冲程”模型提出mHsp70发生构象变化，从而主动将前体链拉过孔。在此我们对这两种模型进行定量阐述，并根据最近的实验证据（即前体链与转运孔壁强烈相互作用）比较它们的性能。在这些条件下，模拟的布朗棘轮效率低下，而动力冲程机制似乎是对导入过程的合理描述。
