Elastin-like polypeptides (ELP) are environmentally responsive polymers that exhibit phase separation in response to external stimuli such as temperature, pH, light, and ionic strength. It has been shown that the sequence of the pentapeptide, its length, and the solution concentration are very important in the transition of the molecules from soluble to insoluble, but there has not been any detailed study of the effect of molecular architecture on the behavior of ELPs.
In this study we designed, synthesized and characterized ELPs with different architectures and chemical identities to probe the effect of molecular design on the microscopic and macroscopic behavior of ELP molecules and to compare them to the linear ELP molecules. These new architectures also helped us better understand the theory of folding and aggregation of ELPs. The design was based on constructing three-armed star molecules by tagging a trimer forming oligomerization domain to the ELP chains. ELPs were chosen to have different chemical identities by changing the pentapetide sequence. The molecules were synthesized by molecular biology techniques and characterized by different methods.
Our results show that capping the three ELP chains forces the chains to fold into more extended rod-like constructs prior to aggregation. A mathematical model was developed to predict the behavior of ELP chains at the transition temperature and it was shown that there is a difference between N- and C- terminal capping ELPs seem to fold at lower temperatures when their N-termini are held together. It was also shown that the constructs with both their ends capped can be designed such that they fold into a stable unit at much lower temperatures than the linear constructs without necessarily aggregation at higher temperatures.
The trimer constructs were also used to make micellar aggregates that were characterized by dynamic and static light scattering. It was shown that the size of the micelles can be controlled by adjusting salt concentration or by making mixtures of linear and trimer constructs. The micelles were also crosslinked into responsive stable nano-particles.