Striking a balance: mapping the structural stability and mechanical and chemical responsiveness of collagen proteins

多细胞生命是由一些结构构成的，这些结构将细胞维持在所需的位置和组织中。传统上，这些支架被认为是刚性的，在发育过程中铺设的不变的支撑，除非受伤或疾病，否则不会改变。最近的科学进展表明，这些细胞外支架是高度动态的，对其局部微环境的变化做出反应，并将这些变化传达给它们所支持的细胞，而这些细胞反过来又修改这些支架以适应变化的环境。在人类（以及所有多细胞动物）中，这些支架的主要成分是一种叫做胶原蛋白的蛋白质（来自法语“coller”或to glue）。在其最小（分子）水平上，这种蛋白质具有独特的三螺旋结构，三条链相互缠绕形成一个长长的右旋螺旋。胶原蛋白在细胞内生成，然后在细胞外组装成各种各样的高阶结构，形成支持多种功能的环境特异性支架。例如，胶原形成肌腱的绳状结构，类似的组织模板骨的矿化；它们也可以形成支持我们组织外围细胞的网络，将“内部”与“外部”分开，也可以形成肾脏的过滤屏障。机械生物学领域的迅速发展表明，细胞对细胞外环境的力学作出反应；例如，当干细胞生长在坚硬和柔软的表面上时，它们会分化成骨细胞和脂肪细胞。目前尚不清楚的是细胞外环境是如何将这些信息传递给细胞的。由于胶原蛋白占主导地位（占我们体内蛋白质的四分之一以上），我们的目标是了解胶原蛋白如何感知和传达其局部环境中的机械和化学变化。我的研究小组在胶原蛋白表征方面具有国际独特的技能，使我们能够探索单个胶原蛋白的力学特性。我们通过单分子成像（使用原子力显微镜技术）和单分子力光谱（使用离心力显微镜新技术）的结合来做到这一点。我们的目标是了解沿着胶原蛋白三螺旋长度的序列可变性是如何被用来传达化学环境的变化（例如，在细胞分泌或骨降解和癌症转移等生物过程中发生的变化）和机械应变（例如，在我们采取的每一步中发生的变化或细胞在细胞外基质上的拉扯）。我的研究小组的学生在物理和生物学的界面上获得实验专业知识，在不同的研究团队中发展沟通技巧，并有机会在机械生物学和生物物理学领域建立国际领导地位。

Multicellular life is scaffolded by structures that maintain cells in the desired locations and organizations. Conventionally these scaffolds are viewed as rigid, unchanging supports laid down during development and unaltered except by injury or disease. Recent scientific advances are revealing instead that these extracellular scaffolds are highly dynamic, responsive to changes in their local microenvironment and communicating these changes to the cells they support, which in turn modify these scaffolds to adapt to their changed environment. In humans (and all multicellular animals), the main component of these scaffolds is a protein called collagen (from the French "coller" or to glue). At its smallest (molecular) level, this protein has a unique triple helix structure, with three chains twisting around each other to make a long, right-handed helix. Collagen proteins are made inside cells, then assemble into a wide variety of higher-order structures outside cells to form environment-specific scaffolds supporting a diversity of function. For example, collagens form the rope-like structure of tendon, with similar organizations templating the mineralization of bone; they alternatively can form networks that support cells at the periphery of our tissues, separating "inside" from "outside", and networks that form the filtration barrier of the kidney. The rapidly expanding field of mechanobiology is demonstrating that cells respond to the mechanics of their extracellular environment; for example stem cells differentiate into bone vs. fat cells when grown on a stiff vs. soft surface. What is not clear is how the extracellular environment communicates this information to cells. Because of the predominance of collagen (more than ¼ of the protein in our bodies), we aim to understand how collagen senses and communicates mechanical and chemical changes in its local environment. My research group has developed internationally unique skills in collagen characterization, which enable us to probe the mechanical properties of individual collagen proteins. We do this by a combination of single-molecule imaging (using the technique of atomic force microscopy) and single-molecule force spectroscopy (using a new technique of centrifuge force microscopy). We aim to understand how the sequence variability along the length of collagen's triple helix is used to communicate changes in chemical environment (occurring, for example, during secretion from the cell or in biological processes such as bone degradation and cancer metastasis) and mechanical strain (occurring, for example, with every step we take or by cells tugging at their extracellular matrix). Students in my research group gain experimental expertise at the interface of physics and biology, develop communication skills within a diverse research team, and have the opportunity to build international leadership in the fields of mechanobiology and biophysics.