Molecular rulers to measure membrane thickness in live cells

细胞质膜定义了细胞的边界，许多细胞内部过程被膜结合细胞器划分。膜主要由蛋白质和脂质组成，这是一种小的油腻分子，不能与水很好地混合，导致形成单独的膜结构。细胞产生成千上万种不同化学性质的脂质和蛋白质。生物学家知道为什么细胞会产生这么多不同的蛋白质——它们在细胞内有很多功能。然而，我们不太清楚为什么细胞会如此大量地制造各种不同类型的脂质。其中一个原因可能是脂质改变了细胞膜的结构。这将影响膜的厚度或厚度，膜的弯曲程度以及膜内蛋白质的移动距离和速度。例如，膜结构的变化会影响细胞对信号的反应速度，或者在特定位置可以产生多少特定分子。虽然从概念上讲，膜结构，特别是膜厚度在细胞的功能中是很重要的，但到目前为止，还不可能系统地测量活细胞的膜厚度。我们正在提议开发一种新的化学工具，叫做分子尺子，它将使我们能够测量细胞内部和外部膜的厚度。我们的工具将使用工程DNA作为支架，因为它具有精确定义的尺寸，并且可以将其他化学物质附着在上面。我们将用类脂分子覆盖部分DNA，使其能够移动到膜中。我们还会在特定的距离上将染料彼此连接起来。其中一种染料会根据它是在膜内还是在膜外而改变亮度和颜色。由于我们将合成具有特定尺寸的分子尺，我们可以使用显微镜来检测染料亮度的变化，并得出膜在特定位置的厚度。然后，我们计划使用这些工具来了解细胞如何以及为什么在不同位置改变它们的膜厚度。

The plasma membrane defines the boundary of a cell, and many internal cellular processes are compartmentalised by membrane-bound organelles. Membranes are primarily composed of proteins and lipids, which are small greasy molecules that do not mix well with water, leading to the formation of separate membrane structures. Cells make many thousands of lipids and proteins that are chemically distinct. Biologists know why cells make so many different proteins - they have many functions within cells. However, it is less clear why cells invest so heavily into making many different types of lipids. One reason could be that lipids change the architecture of the membrane. This would affect how thick or thin the membrane is, how much it can bend and how far or rapidly proteins within the membrane can move. Changes in membrane architecture would affect, for example, how quickly a cell would be able to respond to a signal, or how much of a certain molecule it could make in a specific location. Although conceptually it is clear that membrane architecture, and specifically membrane thickness must be important in how the cell functions, it has so far not been possible to measure membrane thickness systematically in live human cells. We are proposing to develop new chemical tools, called molecular rulers, that will allow us to measure how thick membranes are inside and at the exterior of cells. Our tools will use engineered DNA as a scaffold because it has precisely defined dimensions and it is possible to attach other chemicals to it. We will cloak part of the DNA with lipid-like molecules to allow it to move into membranes. We will also attach dyes at specific distances to each other. One of the dyes will change in brightness and colour depending on if it is inside or outside of a membrane. Since we will synthesise the molecular rulers with specific dimensions, we can use microscopy to detect changes in dye brightness and conclude how thick the membrane is at a specific location. We then plan to use the tools to understand how and why cells change their membrane thickness at different locations.