J Savage, M Ney, A Chilkoti
Biomedical Engineering; Duke University; Durham, NC 27708
Elastin-like polypeptides (ELPs) have the ability to phase separate in liquid which provides many applications (like protein purification), and with modifications they can have pH dependent properties to form functional materials. ELPs reversibly change solubility based on temperature, becoming insoluble after reaching a critical solution temperature. CDC-19 amyloids are found in yeast and sequester proteins during stress. When added to ELPs, the ELPs become irreversible below a certain pH threshold. However, this threshold is below physiological conditions and pH changes alter ELP transition temperatures, limiting use and predictability. It was hypothesized that 1) substituting the aromatic amino acids will increase the threshold pH and 2) adding positively charged amino acids to neutralize the amyloid’s negative charge will stabilize the phase transition temperature across pHs. Polypeptides were placed into a UV-Vis spectrophotometer at various pHs, then heated and cooled to record transition behavior and measure phase reversibility. Polypeptides were also imaged under a microscope to show phase behavior assemblies (such as droplets and solids) at different pHs. It was found that the substitution of aromatic amino acids increases the pH threshold of polypeptides. In contrast, the addition of positively charged amino acids, arginine and lysine, abolished pH sensitivity. A material that is pH sensitive potentially has many applications, such as researching cancer as cancerous cells have distinct pHs. Future research should seek to increase the pH at which the ELPs change to a physiological one and stabilize the temperature-dependent behavior at various pHs.
