Quantitative Model of the Phase Behavior of Recombinant pH-Responsive Elastin-Like Polypeptides

Abstract

Quantitative models are required to engineer biomaterials with environmentally responsive properties. With this goal in mind, we developed a model that describes the pH dependent phase behavior of a class of stimulus responsive elastin-like polypeptides (ELPs) that undergo reversible phase separation in response to their solution environment. Under isothermal conditions, charged ELPs can undergo phase separation when their charge is neutralized. Optimization of this behavior has been challenging because the pH at which they phase separate, pHt, depends on their composition, molecular weight, concentration, and temperature. To address this problem, we developed a quantitative model to describe the phase behavior of charged ELPs that uses the Henderson-Hasselbalch relationship to describe the effect of side-chain ionization on the phase transition temperature of an ELP. The model was validated with pH-responsive ELPs that contained either acidic (Glu) or basic (His) residues. The phase separation of both ELPs fit this model across a range of pH. These results have important implications for applications of pH-responsive elastin-like polypeptides, because they provide a quantitative model for the rational design of pH responsive polypeptides whose transition can be triggered at a specified pH.

Postnatal Pancreas of Mice Contains Tripotent Progenitors Capable of Giving Rise to Duct, Acinar, and Endocrine Cells In Vitro

“…We previously incorporated the IKVAV sequence into an elastin-based artificial extracellular matrix (aECM) protein [35][36][37]. Elastin was used for several practical reasons: (1) as an ECM protein, it mimics the rigidity of soft tissue, (2) physical properties of the hybrid aECM protein such as solubility and pH responsiveness can be controlled by varying the elastin sequence [38,39] without perturbation of the IKVAV sequence, and (3) because elastins are thermally responsive, the hybrid aECM protein can be purified by repeated thermal cycling. This method, called ''inverse temperature cycling,'' is a low cost, technically simple approach for purifying large quantities of recombinant proteins made in bacterial expression systems [38].…”

Tuning Thermoresponsive Properties of Cationic Elastin-like Polypeptides by Varying Counterions and Side-Chains

“…molecular weight), which are two parameters exquisitely controlled by the initial gene design. 10,11,12 Although recombinant DNA and protein engineering techniques are powerful methods to access precision protein-like polymers, tedious molecular cloning steps can sometimes hamper the development of large libraries of ELPs with different sizes, diverse functionalities and tunable properties. Moreover, some functional groups can only be introduced by the use of unnatural amino acids, which in general significantly lower the production yields.…”

Applications of elastin-like polypeptides in drug delivery

“…Most notably, kosmotropic salts (Cl − and higher on the Hofmeister scale of anions) depress the ELP T t , with increasing concentration of salt enhancing this effect [7]. Furthermore, the local pH can influence the T t of ELP sequences that include ionizable guest residues [8, 9]. …”