Effects Of Biocompatible Interfaces/Small Molecules On Lysozyme Crystallization

In the field of food and biopharmaceutical,the desirable nucleants should be biocompatible,non-toxic and harmless to human body and environment except of regulating the protein crystallization.Therefore,exploring potential biocompatible nucleating agents is crucial for expanding the application of protein crystals.In this paper,polycaprolactone(PCL)-based hydrophobic biopolymers(PCL-TA,PCL-BDO)were synthesized by incorporating tannic acid(TA)or 1,4-butanediol(BDO)into the chain of PCL,and studied the effects on the crystallization of lysozyme.The results of water contact angle measurement and zeta potential show that the hydrophobicity of two PCL-based polymers are approximate,and PCL-TA has more negative charges than PCL-BDO.The crystallization experiment shows that the number of crystals on PCL-TA is greatly reduced and the size is increased(more than 60 %crystals were larger than 300 ?m),whereas on the surface of PCL-BDO the number of crystals is basically unchanged while the size is slightly increased.Heterogeneous nucleation of lysozyme crystals was significantly affected by the surface functional groups of the polymers.Combined with molecular simulation studies,it is shown that the introduction of TA structural units does enhance the interaction between the PCLTA interface and lysozyme protein molecules,which accelerate the crystal growth on PCL-TA.On the other hand,adopting glutathione(GSH),glycine(Gly)and cysteine(Cys)as the additive,the lysozyme crystallization was investigated using the droplet vapor diffusion,with a view to exploring nucleating agents with good biocompatibility.Characterized by FTIR,PXRD,CD,etc.,the results show that GSH can effectively promote protein crystallization under even lower lysozyme concentration via increasing nucleation rate,comparing with Gly and Cys;while the structures of lysozyme crystals generated in the presence of the biomolecular additives are similar with those in the absence of the additives.In combination with molecular modeling,it illustrates that the stronger interactions between small biomolecular additives and the lysozyme loop accelerate the heterogeneous nucleation obviously.