Protein adsorption in porous adsorbent particles: A multiscale modeling study on inner radial humps in the concentration profiles of adsorbed protein induced by nonuniform ligand density distributions

Tailored nanodisc immobilization for one-step purification and reconstitution of cytochrome P450: A tool for membrane proteins' hard cases

A novel nanodisc-based immobilization method was developed for high-efficient purification and reconstitution of cytochrome P450 in one step. Using membrane scaffold protein containing a histidine tag, charged-nanodiscs were prepared in the form of self-assembly of lipid-protein nanoparticles. Their properties including the particle diameter and its distribution and Zeta potential were controlled well by adjusting molar ratios of phospholipids to membrane scaffold protein. At an optimum lipid-to-membrane scaffold protein molar ratio of 60:1, uniformly regular-shaped and discoidal nanodiscs with an average particle diameter of 10 nm and Zeta potential of -19 mV were obtained. They can be well fractionated by size exclusion chromatography. Charged-nanodiscs were successfully immobilized onto Ni-chelating microspheres via histidine tags with a density of 6.6 mg membrane scaffold protein/mL gel. After being packed in a column, chromatography studies demonstrated that this nanodisc-immobilized chromatographic medium had a specific binding to cytochrome P450 in rat liver microsome. Nanodiscs containing cytochrome P450 can be furthermore eluted from the column with a diameter of about 87.0 nm and height of about 8.0 nm, respectively. The purity of cytochrome P450 after purification increased 25 folds strikingly. This nanodisc-immobilized chromatography method is promising for the one-step purification and reconstitution of membrane protein.

Molecular modeling of polymeric adsorbent media: the effects of counter-ions on ligand immobilization and pore structure

Molecular dynamics modeling and simulations are employed to study the immobilization of ligands on the surface of the pores of a base porous polymeric matrix. The results show the significant effects that the counter-ions have on the spatial distribution of the density of immobilized ligands as well as on the pore size and pore connectivity distributions of the porous adsorbent medium being constructed. The results for the systems studied in this work indicate that by using doubly charged counter-ions whose numbers during ligand immobilization are half to those of singly charged counter-ions, the ligand immobilization process proceeds faster and the magnitude of local nonelectroneutrality becomes smaller. More importantly, the pore structures of the adsorbent media resulting from the system using doubly charged counter-ions have porous structures that are characterized by more mid-sized pores and higher pore connectivity than the porous adsorbent structures generated by the system employing singly charged counter-ions and, furthermore, the density distribution of the immobilized ligands in the porous structures where doubly charged counter-ions are employed tends to be more uniform laterally and the ligands are surrounded by fewer counter-ions. These characteristics affected by the use of doubly charged counter-ions could provide important advantages with respect to the transport and adsorption of adsorbate biomolecules of interest. Furthermore, the results of this work indicate that the type of counter-ions being used in the ligand immobilization process could represent an additional control variable for affecting the ligand density distribution as well as the pore size and pore connectivity distributions of the porous structure of the adsorbent medium being constructed.