Nonmechanical Protein Can Have Significant Mechanical Stability

摘要

Many proteins function as complex mechanochemical machinery in living cells to constantly sense, generate, and bear mechanical forces.[1] In addition to their biological importance, these mechanical proteins also arouse tremendous interest in nanoscience and technology and have been incorporated into nanomechanical devices for well-defined applications.[2]-[4] It is clear that these mechanical proteins will find a wide range of applications as building blocks for the bottom-up construction of functional nanomechanical devices.[4], [5] Elastomeric proteins are a special class of mechanical proteins.[6] They are placed under mechanical tension under physiological conditions and serve as molecular springs in a variety of biological machines and tissues to establish elastic connections and provide mechanical strength, elasticity, and extensibility.[6]-[13] Recent developments in single-molecule force spectroscopy have enabled the direct measurement of the mechanical stability and elasticity of elastomeric proteins at the single-molecule level.[7]-[10], [13]-[16] Combined with molecular dynamics (MD) simulations, single-molecule atomic force microscopy (AFM) studies have revealed rich information about the mechanical architecture and design of elastomeric proteins.[14], [17]-[23] Compared with proteins that commonly do not bear any mechanical functions under physiological conditions, mechanical proteins are just a small fraction of the total proteins inside cells. To construct multifunctional nanomechanical devices, it is desirable to extend single-molecule force-spectroscopic studies to include nonmechanical proteins (such as enzymes), as the abundant nonmechanical proteins may significantly expand the tool box of mechanical proteins, impart novel functionality, and enable applications such as force sensors[24] and switches. A prerequisite for these applications is that these nonmechanical proteins can withstand mechanical tension. It has been proposed that nonmechanical proteins may contain motifs of considerable mechanical stability;[25] however, most of the nonmechanical proteins that have been studied so far, such as barnase and carmodulin, are mechanically labile and only have marginal mechanical stability.[24], [26]-[30] Green fluorescent protein (GFP) is the strongest nonmechanical protein to date and has a mechanical stability of approximately 100 pN.[24] It remains a question whether nonmechanical proteins can have sufficient mechanical stability and be used for mechanical applications. Herein, we use single-molecule AFM and protein engineering to demonstrate that nonmechanical proteins, with desired structure and topology, can have significant mechanical stability.