Department of Bioengineering, University of California, Los Angeles, Los Angeles, California 90025, United States.
Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States.
ACS Nano. 2024 Jun 18;18(24):15545-15556. doi: 10.1021/acsnano.4c00277. Epub 2024 Jun 5.
Deterministic formation of membrane scission necks by protein machinery with multiplexed functions is critical in biology. A microbial example is M2 viroporin, a proton pump from the influenza A virus that is multiplexed with membrane remodeling activity to induce budding and scission in the host membrane during viral maturation. In comparison, the dynamin family constitutes a class of eukaryotic proteins implicated in mitochondrial fission, as well as various budding and endocytosis pathways. In the case of Dnm1, the mitochondrial fission protein in yeast, the membrane remodeling activity is multiplexed with mechanoenzyme activity to create fission necks. It is not clear why these functions are combined in these scission processes, which occur in drastically different compositions and solution conditions. In general, direct experimental access to changing neck sizes induced by individual proteins or peptide fragments is challenging due to the nanoscale dimensions and influence of thermal fluctuations. Here, we use a mechanical model to estimate the size of scission necks by leveraging small-angle X-ray scattering structural data of protein-lipid systems under different conditions. The influence of interfacial tension, lipid composition, and membrane budding morphology on the size of the induced scission necks is systematically investigated using our data and molecular dynamic simulations. We find that the M2 budding protein from the influenza A virus has robust pH-dependent membrane activity that induces nanoscopic necks within the range of spontaneous hemifission for a broad range of lipid compositions. In contrast, the sizes of scission necks generated by mitochondrial fission proteins strongly depend on lipid composition, which suggests a role for mechanical constriction.
蛋白质机器的确定性形成的膜缢痕颈部在生物学中具有多种功能，这是至关重要的。一个微生物的例子是 M2 病毒孔蛋白，它是来自甲型流感病毒的质子泵，具有膜重塑活性，可在病毒成熟过程中诱导宿主膜出芽和缢痕。相比之下，动力蛋白家族构成了一类涉及线粒体裂变以及各种出芽和内吞作用途径的真核蛋白。在酵母中线粒体裂变蛋白 Dnm1 的情况下，膜重塑活性与机械酶活性相结合，形成裂变颈。目前尚不清楚为什么这些功能会在这些发生在截然不同组成和溶液条件下的裂变过程中结合在一起。一般来说，由于纳米级尺寸和热涨落的影响，直接实验方法很难获得由单个蛋白质或肽片段诱导的颈部尺寸变化。在这里，我们使用机械模型通过利用不同条件下的蛋白-脂质系统的小角度 X 射线散射结构数据来估计缢痕颈部的尺寸。我们使用我们的数据和分子动力学模拟系统地研究了界面张力、脂质组成和膜出芽形态对诱导缢痕颈部尺寸的影响。我们发现甲型流感病毒的 M2 出芽蛋白具有强大的 pH 依赖性膜活性，可在广泛的脂质组成范围内诱导自发半裂变范围内的纳米级颈部。相比之下，线粒体裂变蛋白产生的缢痕颈部的尺寸强烈依赖于脂质组成，这表明机械收缩起着作用。
