Posey Ammon E, Bagheri Mehran, Ross Kyle A, Lanum Elizabeth N, Khan Misha A, Jennings Christine M, Harwig Megan C, Kennedy Nolan W, Hilser Vincent J, Harden James L, Hill R Blake
bioRxiv. 2023 May 29:2023.05.29.542732. doi: 10.1101/2023.05.29.542732.
Dynamins are an essential superfamily of mechanoenzymes that remodel membranes and often contain a "variable domain" (VD) important for regulation. For the mitochondrial fission dynamin, Drp1, a regulatory role for the VD is demonstrated by mutations that can elongate, or fragment, mitochondria. How the VD encodes inhibitory and stimulatory activity is unclear. Here, isolated VD is shown to be intrinsically disordered (ID) yet undergoes a cooperative transition in the stabilizing osmolyte TMAO. However, the TMAO stabilized state is not folded and surprisingly appears as a condensed state. Other co-solutes including known molecular crowder Ficoll PM 70, also induce a condensed state. Fluorescence recovery after photobleaching experiments reveal this state to be liquid-like indicating the VD undergoes a liquid-liquid phase separation under crowding conditions. These crowding conditions also enhance binding to cardiolipin, a mitochondrial lipid, raising the possibility that phase separation may enable rapid tuning of Drp1 assembly necessary for fission.
发动蛋白是一类重要的机械酶超家族，可重塑膜结构，通常包含一个对调节至关重要的“可变结构域”（VD）。对于线粒体分裂发动蛋白Drp1而言，能使线粒体延长或碎片化的突变证明了VD的调节作用。VD如何编码抑制和刺激活性尚不清楚。在这里，分离出的VD显示为内在无序（ID），但在稳定渗透压剂TMAO中会发生协同转变。然而，TMAO稳定状态并未折叠，令人惊讶的是呈现为凝聚状态。包括已知的分子拥挤剂聚蔗糖PM 70在内的其他共溶质也会诱导凝聚状态。光漂白后荧光恢复实验表明这种状态呈液体状，表明VD在拥挤条件下会发生液-液相分离。这些拥挤条件还增强了与心磷脂（一种线粒体脂质）的结合，增加了相分离可能使裂变所需的Drp1组装得以快速调节的可能性。
