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The outstanding rubber-like elasticity of resilin and resilin-mimetic proteins depends critically on the level of hydration. In this investigation, water vapor sorption and the role of hydration on the molecular chain dynamics and viscoelastic properties of resilin-mimetic protein, rec1-resilin is investigated in detail. The dynamic and equilibrium swelling behavior of the crosslinked protein hydrogels with different crosslink density are reported under various controlled environments. We propose three different stages of hydration; involving non-crystallizable water, followed by condensation or clustering of water around the already hydrated sites, and finally crystallizable water. The kinetics of water sorption for this engineering protein is observed to be comparable to hydrophilic polymers with a diffusion coefficient in the range of 10 7 cm2 s 1. From the comparison between the absorption and desorption isotherms at a constant water activity, it has been observed that rec1-resilin exhibits sorption hysteresis only for the tightly bound water. Investigation of molecular mobility using differential scanning calorimetry, indicates that dehydrated crosslinked rec1-resilin is brittle with a glass transition temperature (Tg) of >180 C, which dramatically decreases with increasing hydration; and above a critical level of hydration rec1-resilin exhibits rubber-like elasticity. Nanoindentation studies show that even with little hydration (

In this investigation, for the first time we report the effects of pH on the molecular orientation, packing density, structural properties, adsorption characteristics and viscoelastic behaviour of resilin-mimetic protein rec1 - resilin at the solid–liquid interface using quartz crystal microbalance with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR) spectroscopy. QCM-D and SPR data confirm that the binding ability of rec1 - resilin on a substrate is strongly pH-dependent the protein packing density on a gold surface is calculated to be 4.45 × 10 13 per cm 2 at the isoelectric point (IEP ∼ 4.9), 8.79 × 10 11 per cm 2 at pH 2 and 9.90 × 10 11 per cm 2 at pH 12, respectively. Our findings based on the thickness, dissipation and viscoelasticity of the rec1 - resilin adlayer also indicate that it is adsorbed onto the gold substrate with different orientation depending on pH, such as back-on adsorption at acidic pH of 2, compact end-on bilayer adsorption at the IEP and side-on at high alkaline pH of 12. When rec1 - resilin is ‘pinned’ to the substrate at IEP and subsequently exposed to an electrolyte solution adjusted to different pH, it switches from a compact globular conformation of the bio-macromolecule at the IEP to a coil conformation at pH between IEP to IED (IED = pKa value of tyrosine amino acid residue) and an extended coil conformation at pH > IED. This transformation from globule to coil to extended coil conformation is kinetically fast, robust and completely reversible. Such responsive surfaces created using ‘smart’ biomimetic rec1 - resilin have the potential to find applications in many areas including biotechnology, medicine, sensors, controlled drug delivery systems and engineering.

Protein adsorption on surfaces is a fundamental step in many applications. While various methods such as lithography, self assembly using nanoparticles, layer-by-layer attachment, etc. have been employed, here we report fabrication of controlled nanostructure of a new resilin-mimetic elastic protein rec1-resilin using physical approaches. We investigate the assembly, morphology and tunability of the nanostructure of adsorbed rec1-resilin architectures by atomic force microscopy (AFM) and scanning thermal microscopy (SThm) demonstrating that the protein conformation and structure during assembly can be controlled by tuning the physical conditions at the surface. Our findings show distinct morphology and height of monomolecular rec1-resilin film, dependent on substrate surface energy. We also show that these heights, a function of molecular orientation, can be maintained on swelling and drying. Refereed/Peer-reviewed