Light Scattering Study of the Size and Shape of Mixed Elastin-Like Polypeptide Micelles

Elastin-Like Polypeptides (ELP) formed thermoreversible nanoparticles by having three-armed star polypeptides (each with 20 repeats of (GVGVP) amino acid sequence) extending from the negatively charged foldon domain. In addition, linear constructs composed of 40 repeats of the (GVGVP) sequence were introduced into the system. The mixed ELP polymer system is soluble at room temperature and becomes insoluble at ~ 50 forming micelles with the foldons on the exterior and linear constructs at the core. Above the transition, the size and shape of the mixed micelles are dependent on the pH of the solution, concentration of the PBS, and the ratio of the linear to foldon concentration. The Depolarized Dynamic Light Scattering was employed to study the structure and dynamics of the mixed micelles at 62 ^oC and pH of 7.3 - 7.5. The ELP foldon micelles have a radius of 10nm; the introduction of the linear ELP chains leads to a growth of mixed micelles at a linear rate, at fixed PBS and foldon concentrations. A developed molar volumes model explains the linear size growth of the mixed system. Static Light Scattering results largely support the model. However, the apparent VH signal found can indicate elongation in geometry of the particles or anisotropic properties of the micelle core.