Effects Of Charged Polymers On Protein Crystallization

The study on the nucleation and growth of protein crystals is of great significance for the research and development of protein separation and purification technology and biopharmaceutical technology.Polyamino acid is a kind of amino acid polymer,which has good biocompatibility and is non-toxic and harmless,especially for drug release.The effects of poly-?-glutamic acid(PGA)and poly-?-lysine(PL)on nucleation and growth of protein crystals were studied.Firstly,the protein was screened.Lysozyme,thaumatin,concanavalin A and catalase were selected as the model protein for the crystallization experiment.According to the crystal size,protein structure and electrification characteristics,lysozyme and thaumatin were selected for the follow-up experimental study.Secondly,crystallization experiments were carried out under the conditions of adding PGA(negative polymer)and PL(positive polymer),respectively,to study the influence of the added polymer on the crystal size and quantity of lysozyme.Through the characterization of circular dichroism spectrum,dynamic light scattering,zeta potential and so on,it was found that the charged polymer can promote the heterogeneous nucleation of proteins,in particular,the addition of PGA can promote the low concentration of lysozyme(5 mg/m L)to produce more crystals.Both of these additives can significantly enhance the heterogeneous nucleation of lysozyme.Thus,we chose different charged characteristics of lysozyme segments(SEG1,SEG2,SEG3),adopt the method of molecular simulation to explore the lysozyme and the interaction between charged polymer.The results showed that the spatial order of binding energy of PGA and lysozyme segments was monotonously changed compared with PL,make the structure of the complex of PGA and lysozyme molecules more compact,which is favorable for crystal nucleation.On the other hand,PGA and PL were used as additives to study its effect on thaumatin crystallization.It was found that the addition of the charged polymer canmake the crystal of the sweet protein larger,and the effect of PGA to make the crystal larger is better than PL.Combined with dynamic light scattering,zeta potential characterization,and molecular modeling studies,the effects of different charged polymers on the nucleation of thaumatin crystals were revealed.