Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, CA 94720.
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
Proc Natl Acad Sci U S A. 2022 Aug 9;119(32):e2200019119. doi: 10.1073/pnas.2200019119. Epub 2022 Aug 1.
The nanoscale structure and dynamics of proteins on surfaces has been extensively studied using various imaging techniques, such as transmission electron microscopy and atomic force microscopy (AFM) in liquid environments. These powerful imaging techniques, however, can potentially damage or perturb delicate biological material and do not provide chemical information, which prevents a fundamental understanding of the dynamic processes underlying their evolution under physiological conditions. Here, we use a platform developed in our laboratory that enables acquisition of infrared (IR) spectroscopy and AFM images of biological material in physiological liquids with nanometer resolution in a cell closed by atomically thin graphene membranes transparent to IR photons. In this work, we studied the self-assembly process of S-layer proteins at the graphene-aqueous solution interface. The graphene acts also as the membrane separating the solution containing the proteins and Ca ions from the AFM tip, thus eliminating sample damage and contamination effects. The formation of S-layer protein lattices and their structural evolution was monitored by AFM and by recording the amide I and II IR absorption bands, which reveal the noncovalent interaction between proteins and their response to the environment, including ionic strength and solvation. Our measurement platform opens unique opportunities to study biological material and soft materials in general.
已经使用各种成像技术（例如在液体环境中的透射电子显微镜和原子力显微镜（AFM））广泛研究了表面上蛋白质的纳米级结构和动力学。这些强大的成像技术可能会潜在地损坏或干扰精细的生物材料，并且不提供化学信息，这阻止了对其在生理条件下演变的基础动态过程的基本理解。在这里，我们使用我们实验室开发的平台，该平台可在原子层厚的石墨烯膜透明的红外（IR）光子的细胞中以纳米级分辨率在生理液体中获取生物材料的红外（IR）光谱和 AFM 图像。在这项工作中，我们研究了 S-层蛋白在石墨烯-水溶液界面处的自组装过程。石墨烯还充当了将含有蛋白质和 Ca 离子的溶液与 AFM 尖端隔开的膜，从而消除了样品损坏和污染的影响。通过 AFM 和记录酰胺 I 和 II IR 吸收带监测 S-层蛋白晶格的形成及其结构演变，这揭示了蛋白质之间的非共价相互作用及其对环境的响应，包括离子强度和溶剂化。我们的测量平台为研究生物材料和一般软材料提供了独特的机会。
