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Abstract：
ICA512/PTPRN is a receptor tyrosine-like phosphatase implicated in the biogenesis and turnover of the insulin secretory granules (SGs) in pancreatic islet beta cells. Previously we found biophysical evidence that its luminal RESP18 homology domain (RESP18HD) forms a biomolecular condensate and interacts with insulin in vitro at close-to-neutral pH, that is, in conditions resembling those present in the early secretory pathway. Here we provide further evidence for the relevance of these findings by showing that at pH 6.8 RESP18HD interacts also with proinsulin-the physiological insulin precursor found in the early secretory pathway and the major luminal cargo of β-cell nascent SGs. Our light scattering analyses indicate that RESP18HD and proinsulin, but also insulin, populate nanocondensates ranging in size from 15 to 300 nm and 10e2 to 10e6 molecules. Co-condensation of RESP18HD with proinsulin/insulin transforms the initial nanocondensates into microcondensates (size >1 μm). The intrinsic tendency of proinsulin to self-condensate implies that, in the ER, a chaperoning mechanism must arrest its spontaneous intermolecular condensation to allow for proper intramolecular folding. These data further suggest that proinsulin is an early driver of insulin SG biogenesis, in a process in which its co-condensation with RESP18HD participates in their phase separation from other secretory proteins in transit through the same compartments but destined to other routes. Through the cytosolic tail of ICA512, proinsulin co-condensation with RESP18HD may further orchestrate the recruitment of cytosolic factors involved in membrane budding and fission of transport vesicles and nascent SGs.
摘要：
ICA512/PTPRN是一种受体酪氨酸样磷酸酶，与胰岛β细胞中胰岛素分泌颗粒（SGs）的生物发生和周转有关。以前，我们发现生物物理证据表明其腔RESP18同源域（RESP18HD）形成生物分子缩合物，并在接近中性pH下与胰岛素相互作用，即，在类似于早期分泌途径中存在的条件下。在这里，我们通过显示在pH6.8时RESP18HD还与胰岛素原相互作用，为这些发现的相关性提供了进一步的证据-胰岛素原是在早期分泌途径中发现的生理胰岛素前体和β细胞新生SGs的主要管腔货物。我们的光散射分析表明RESP18HD和胰岛素原，还有胰岛素，填充大小从15到300nm和10e2到10e6分子的纳米缩合物。RESP18HD与胰岛素原/胰岛素的共缩合将初始纳米缩合物转化为微缩合物(尺寸>1μm)。胰岛素原自凝集的内在趋势意味着，在ER,伴侣机制必须阻止其自发的分子间缩合，以允许适当的分子内折叠。这些数据进一步表明，胰岛素原是胰岛素SG生物发生的早期驱动因素，在与RESP18HD共缩合的过程中，参与了它们与其他分泌蛋白的相分离，这些蛋白通过相同的隔室运输，但去往其他途径。通过ICA512的胞质尾部，胰岛素原与RESP18HD的共缩合可以进一步协调参与运输囊泡和新生SGs的膜出芽和裂变的胞质因子的募集。本文受版权保护。保留所有权利。
