Complex of human apolipoprotein C-1 with phospholipid: Thermodynamic or kinetic stability?
Complex of human apolipoprotein C-1 with phospholipid: Thermodynamic or kinetic stability?
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DOI：
10.1021/bi025588w
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发表时间：
2002-06-11
期刊：
影响因子：
2.9
通讯作者：
Gantz, DL
中科院分区：
文献类型：
--
作者：
Gursky, O;Ranjana;Gantz, DL
载脂蛋白 (apo) C-1 与二肉豆蔻酰磷脂酰胆碱 (DMPC) 的盘状复合物的热展开揭示了一种基于动力学而不是热力学的脂蛋白稳定的新机制。以 0.047 至 1.34 K/min 的几种加热/冷却速率记录的远紫外 CD 熔化曲线显示出缓慢非平衡转变的滞后和扫描速率依赖性特征。在缓慢的加热速率下，复合物中的 apoC-1 解折叠开始于 25 摄氏度以上，表观解链温度 T-m 类似于 48 +/- 1.5 摄氏度，接近游离蛋白的 T-m = 51 +/- 1.5 摄氏度。因此，DMPC 结合可能不会显着增加 apoC-1、DeltaG(25 ℃) < 2 kcal/mol 的低表观热力学稳定性。 T-m 的扫描速率依赖性和动力学数据的阿伦尼乌斯分析表明活化焓 E-a = 25 +/- 5 kcal/mol，这为盘上展开的蛋白质的自由能垒提供了主要贡献，DeltaG* 大于或等于 17 kcal/mol。因此，apoC-1/DMPC 盘在动力学上稳定，但在热力学上不稳定。为了探索这种动力学稳定性的起源，我们利用 CD 实验中测量的倍增电极电压，该电压显示了 apoC-1/DMPC 复合物的紫外光散射（d 类似于 20 nm）的温度依赖性贡献。在 222 nm 处记录的 CD 和打拿极电压熔解曲线的相关性表明蛋白质解折叠与复杂尺寸和/或层状结构的增加之间的紧密耦合，表明焓屏障是由盘与囊泡融合时脂质堆积相互作用的瞬时破坏引起的。我们假设动力学机制可能提供脂蛋白稳定的一般策略，在缺乏高包装特异性的情况下促进复合物的稳定性和成分变异性。
Thermal unfolding of discoidal complexes of apolipoprotein (apo) C-1 with dimyristoyl phosphatidylcholine (DMPC) reveals a novel mechanism of lipoprotein stabilization that is based on kinetics rather than thermodynamics. Far-UV CD melting curves recorded at several heating/cooling rates from 0.047 to 1.34 K/min show hysteresis and scan rate dependence characteristic of slow nonequilibrium transitions. At slow heating rates, the apoC-1 unfolding in the complexes starts just above 25 degreesC and has an apparent melting temperature T-m similar to 48 +/- 1.5 degreesC, close to T-m = 51 +/- 1.5 degreesC of free protein. Thus, DMPC binding may not substantially increase the low apparent thermodynamic stability of apoC-1, DeltaG(25 degreesC) < 2 kcal/mol. The scan rate dependence of T-m and Arrhenius analysis of the kinetic data suggest an activation enthalpy E-a = 25 +/- 5 kcal/mol that provides the major contribution to the free energy barrier for the protein unfolding on the disk, DeltaG* greater than or equal to 17 kcal/mol. Consequently, apoC-1/DMPC disks are kinetically but not thermodynamically stable. To explore the origins of this kinetic stability, we utilized dynode voltage measured in CD experiments that shows temperature-dependent contribution from UV light scattering of apoC-1/DMPC complexes (d similar to 20 nm). Correlation of CD and dynode voltage melting curves recorded at 222 nm indicates close coupling between protein unfolding and an increase in the complex size and/or lamellar structure, suggesting that the enthalpic barrier arises from transient disruption of lipid packing interactions upon disk-to-vesicle fusion. We hypothesize that a kinetic mechanism may provide a general strategy for lipoprotein stabilization that facilitates complex stability and compositional variability in the absence of high packing specificity.