Bragg Institute, Australian Nuclear Science and Technology Organisation, New South Wales, Australia; School of Molecular Bioscience, The University of Sydney, New South Wales, Australia.
School of Molecular Bioscience, The University of Sydney, New South Wales, Australia.
Biophys J. 2012 Aug 8;103(3):541-549. doi: 10.1016/j.bpj.2012.06.042.
Calmodulin (CaM) expression is upregulated upon HIV-1 infection and interacts with proteins involved in viral processing, including the multifunctional HIV-1 MA protein. We present here the results of studies utilizing small-angle neutron scattering with contrast variation that, when considered in the light of earlier fluorescence and NMR data, show CaM binds MA in an extended open-clamp conformation via interactions with two tryptophans that are widely spaced in sequence and space. The interaction requires a disruption of the MA tertiary fold such that MA becomes highly extended in a long snakelike conformation. The CaM-MA interface is extensive, covering ~70% of the length of the MA such that regions known to be important in MA interactions with critical binding partners would be impacted. The CaM conformation is semiextended and as such is distinct from the classical CaM-collapse about short α-helical targets. NMR data show that upon dissociation of the CaM-MA complex, either by the removal of Ca or increasing ionic strength, MA reforms its native tertiary contacts. Thus, we observe a high level of structural plasticity in MA that may facilitate regulation of its activities via intracellular Ca-signaling during viral processing.
钙调蛋白（CaM）的表达在 HIV-1 感染后上调，并与参与病毒加工的蛋白质相互作用，包括多功能 HIV-1 MA 蛋白。我们在这里展示了利用对比变化的小角度中子散射进行研究的结果，这些结果结合早期的荧光和 NMR 数据表明，CaM 通过与两个在序列和空间上广泛间隔的色氨酸相互作用，以扩展的开放夹构象结合 MA。这种相互作用需要破坏 MA 的三级折叠，使 MA 呈现出长蛇形的高度伸展构象。CaM-MA 界面广泛，覆盖 MA 长度的约 70%，因此，已知在 MA 与关键结合伴侣相互作用中重要的区域将受到影响。CaM 的构象是半伸展的，因此与经典的 CaM 对短 α-螺旋靶标的折叠不同。NMR 数据表明，当 CaM-MA 复合物解离时，无论是通过去除 Ca 还是增加离子强度，MA 都会重新形成其天然的三级接触。因此，我们观察到 MA 具有高水平的结构可塑性，这可能有助于通过病毒加工过程中的细胞内 Ca 信号来调节其活性。
