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Abstract：
Plant PIP aquaporins play a central role in controlling plant water status. The current structural model for PIP pH-gating states that the main pH sensor is located in loopD and that all the mobile cytosolic elements participate in a complex interaction network that ensures the closed structure. However, the precise participation of the last part of the C-terminal domain (CT) in PIP pH gating remains unknown. This last part has not been resolved in PIP crystal structures and is a key difference between PIP1 and PIP2 paralogues. Here, by a combined experimental and computational approach, we provide data about the role of CT in pH gating of Beta vulgaris PIP. We demonstrate that the length of CT and the positive charge located among its last residues modulate the pH at which the open/closed transition occurs. We also postulate a molecular-based mechanism for the differential pH sensing in PIP homo- or heterotetramers by performing atomistic molecular dynamics simulations (MDS) on complete models of PIP tetramers. Our findings show that the last part of CT can affect the environment of loopD pH sensors in the closed state. Results presented herein contribute to the understanding of how the characteristics of CT in PIP channels play a crucial role in determining the pH at which water transport through these channels is blocked, highlighting the relevance of the differentially conserved very last residues in PIP1 and PIP2 paralogues.
摘要：
植物PIP水通道蛋白在控制植物水分状况中起着核心作用。PIPpH门控的当前结构模型指出，主要的pH传感器位于环状D中，并且所有可移动的胞质元素都参与了复杂的相互作用网络，以确保封闭的结构。然而,C末端结构域(CT)的最后部分在PIPpH门控中的确切参与仍然未知.最后一部分在PIP晶体结构中尚未解析,并且是PIP1和PIP2旁系同源物之间的关键区别。这里,通过实验和计算相结合的方法，我们提供了有关CT在寻常βPIPpH门控中的作用的数据。我们证明了CT的长度和位于其最后残基之间的正电荷调节了发生开放/封闭转变的pH。我们还通过对PIP四聚体的完整模型进行原子分子动力学模拟（MDS），为PIP同源或异源四聚体中的差异pH传感提供了基于分子的机制。我们的发现表明，CT的最后一部分会影响处于关闭状态的环形pH传感器的环境。本文提供的结果有助于理解PIP通道中CT的特征如何在确定通过这些通道的水传输被阻断的pH中起关键作用。强调PIP1和PIP2旁系同源物中差异保守的最后一个残基的相关性。
