Interfacial Crystallization and Supramolecular Self-Assembly of Spider Silk Inspired Protein at the Water-Air Interface.

Pezhman Mohammadi,Fabian Zemke,Wolfgang Wagermaier,Markus B Linder

doi:10.3390/ma14154239

Abstract

Macromolecular assembly into complex morphologies and architectural shapes is an area of fundamental research and technological innovation. In this work, we investigate the self-assembly process of recombinantly produced protein inspired by spider silk (spidroin). To elucidate the first steps of the assembly process, we examined highly concentrated and viscous pendant droplets of this protein in air. We show how the protein self-assembles and crystallizes at the water–air interface into a relatively thick and highly elastic skin. Using time-resolved in situ synchrotron x-ray scattering measurements during the drying process, we showed that the skin evolved to contain a high β-sheet amount over time. We also found that β-sheet formation strongly depended on protein concentration and relative humidity. These had a strong influence not only on the amount, but also on the ordering of these structures during the β-sheet formation process. We also showed how the skin around pendant droplets can serve as a reservoir for attaining liquid–liquid phase separation and coacervation from the dilute protein solution. Essentially, this study shows a new assembly route which could be optimized for the synthesis of new materials from a dilute protein solution and determine the properties of the final products.

Highlights

Fabricating materials from biological macromolecules includes utilizing unique molecular interactions to formulate condensed multiscale superstructures
Despite extensive study in recent years, and the fact that spider silk and the spinning process have served as a source of inspiration for the design of next-generation highperformance materials, little is known about the intermediate process steps from dilute spidroin solution to the final dried silk fiber, nor the conformational conversions taking place during this process at ambient conditions [5,6,7,8,9,10]
To better understand the assembly process of the protein at the interface, we vitrified the entire droplets at various time points in liquid ethane–propane (50%:50%) mixture, followed by fracturing the droplets and probing the evolution of the skin using highresolution Scanning Electron Microscopy (SEM) imaging to have direct observation of the assembly

Summary

Introduction

Fabricating materials from biological macromolecules includes utilizing unique molecular interactions to formulate condensed multiscale superstructures. One fascinating example of such ultrastructural material is spider silk, which exhibits exceptional mechanical properties in comparison to any natural or human-made materials. It is a unique material, with high stiffness, strength, and extensibility, and considerable overall toughness [3,4]. Despite extensive study in recent years, and the fact that spider silk and the spinning process have served as a source of inspiration for the design of next-generation highperformance materials, little is known about the intermediate process steps from dilute spidroin solution to the final dried silk fiber, nor the conformational conversions taking place during this process at ambient conditions [5,6,7,8,9,10]. Riekel and Vollrath investigated dragline spider silk strand extracted from living spiders in an in situ X-ray experiment by combining small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS)

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Results

Conclusion