Elcock A H, McCammon J A
Department of Chemistry and Biochemistry, University of California at San Diego, La Jolla 92093-0365, USA.
Biochemistry. 1996 Oct 1;35(39):12652-8. doi: 10.1021/bi9614747.
Brownian dynamics simulations were performed to investigate a possible role for electrostatic channeling in transferring substrate between two of the enzymes of the citric acid cycle. The diffusion of oxaloacetate from one of the active sites of malate dehydrogenase (MDH) to the active sites of citrate synthase (CS) was simulated in the presence and absence of electrostatic forces using a modeled structure for a MDH-CS fusion protein. In the absence of electrostatic forces, fewer than 1% of substrate molecules leaving the MDH active site are transferred to CS. When electrostatic forces are present at zero ionic strength however, around 45% of substrate molecules are successfully channeled. As expected for an electrostatic mechanism of transfer, increasing the ionic strength in the simulations reduces the calculated transfer efficiency. Even at 150 mM however, the inclusion of electrostatic forces results in an increase in transfer efficiency of more than 1 order of magnitude. The simulations therefore provide evidence for the involvement of electrostatic channeling in guiding substrate transfer between two of the enzymes of the citric acid cycle. Similar effects may operate between other members of the citric acid metabolon.
进行了布朗动力学模拟，以研究静电通道在柠檬酸循环的两种酶之间转移底物过程中可能发挥的作用。使用苹果酸脱氢酶（MDH）-柠檬酸合酶（CS）融合蛋白的模型结构，模拟了草酰乙酸在存在和不存在静电力的情况下从苹果酸脱氢酶的一个活性位点扩散到柠檬酸合酶活性位点的过程。在没有静电力的情况下，离开MDH活性位点的底物分子中只有不到1%被转移到CS。然而，当在零离子强度下存在静电力时，约45%的底物分子被成功引导。正如对静电转移机制所预期的那样，模拟中增加离子强度会降低计算出的转移效率。然而，即使在150 mM时，包含静电力也会使转移效率提高超过一个数量级。因此，这些模拟为静电通道参与引导柠檬酸循环的两种酶之间的底物转移提供了证据。类似的效应可能在柠檬酸代谢体的其他成员之间起作用。
