Characterizing Recombinant Spider Wrapping Silk Monomers and Fibers by NMR and AFM

Abstract

Spider silks are among the strongest and toughest naturally produced biomaterials. Despite these appealing properties, very little is known about the mechanisms by which these fibers form or about how fiber structure correlates to mechanical properties. Nuclear magnetic resonance spectroscopy (NMR) and far-ultraviolet circular dichroism (CD) spectroscopy were carried out in the solution-state on monomeric recombinant 13C and 15N labeled wrapping silk protein. This protein is a key constituent of egg case sacs, providing both flexibility and strength, produced in the aciniform spidroin with sequence taken from the spider Argiope trifasciata. Atomic force microscopy (AFM) and fluorescence spectroscopy were performed on manually drawn fibers. Circular dichroism spectroscopy and an initial low-resolution NMR structure both indicate that monomeric aciniform spidroin protein is predominantly α-helical in solution but changes to β-sheet in the fiber, as indicated by thioflavin T fluorescence co-localized with fibers. AFM characterization provides nano-scale surface chemistry and mechanical information for the silk fiber. Our ongoing work is correlating structure to mechanical properties to elucidate the mechanism by which spider silk fibers form.