Conformational Transition of Polyelectrolyte As Influenced by Electrostatic Complexation with Protein

Conformation and conformational transitions are essential for the biological and technological functions of natural polyelectrolytes, for example, DNA. This study aims to clarify how the conformational transition of natural polyelectrolyte is affected and tuned by electrostatic complexation with protein as encountered in many biological processes. A model protein/polyelectrolyte system, beta-lactoglobulin (beta-lg) and kappa-carrageenan (kappa-car), was used for the investigation. The effect was found to be determined by the molecular state of beta-Ig/kappa-car electrostatic complexation and the molecular weight of protein. beta-lg/kappa-car complexation in soluble state had a subtle effect on the coil-to-helix transition of kappa-car, while that in insoluble state greatly suppressed it. On the basis of the McGhee-Hippel theory, a quantitative model was successfully developed to describe the effect of protein/polyelectrolyte electrostatic complexation on the conformational transition of polyelectrolyte. The model can also provide additional information on the change of,tertiary structure of beta-lg upon electrostatic complexation with kappa-car. Moreover, it was found that beta-lg or its hydrolysates with a molecular weight larger than 2000 Da hindered the conformational transition of kappa-car, while those with a molecular weight lower than 1000 Da promoted it. The observations offer a promising approach to control the conformational transition and related properties of polyelectrolytes for technological applications.