Protein Adsorption On Diethylaminoethyl Dextran-grafted Sepharose Gel

Sepharose FF was modified with diethylaminoethyl-dextran(DEAE-dextran,DexD)and/or DEAE(D),and three types of ion exchangers,FF-DexD(grafting-ligand resin),FF-D(surface-ligand resin),and FF-D-Dex D(mixed-ligand resin)were fabricated.To explore roles of grafting-ligand(charged DEAE groups on chains)and surface ligand(charged DEAE groups on surface)on protein adsorption in polymer-functionalized ion-exchangers,their adsorption isotherms and uptake kinetics were investigated using bovine serum albumin(BSA)as the model protein.It was found that both adsorption capacity and uptake rate(effective diffusivity,De)were significantly enhanced by grafting DEAE-dextran chains,and the De values on FF-DexD and FF-D-Dex D(De/D0>1.4)were six times greater than those on FF-D(De/D0<0.3).More importantly,the increase of surface-ligand density also led to the greatly enhanced uptake kinetics on FF-D-DexD.The results indicate that in the mixed-ligand resins,the surface ligands between the neighboring chains,as the “transfer stations”,encouraged the bound protein,which cannot be passed to the next chain directly by the chain swings,to be transferred,resulting in accelerated protein uptake.We further investigated the influences of ionic strength(IS)on the IEC performance of FF-DexD and FF-D-Dex D resins.It was found that adsorption capacities of BSA on DEAE-dextran modified resins(FF-DexD and FF-D-DexD resins)were sharply decreased with increasing IS.Notably,at IS=150 mmol/L NaCl,their adsorption capacities approach to 0 mg/mL.In the broad IS range of 0-100 mmol/L NaCl,the uptake rate of BSA on DEAE-dextran modified resins(De/D0>1.0)was faster than the commercially available non-grafting resin,DEAE Sepharose FF(De/D0<0.6).Moreover,the De values of DEAE-dextran modified resins showed a decreased trend or an increase-then-decrease trend with increasing IS,which were different from that of DEAE Sepharose FF.The different tendency was caused by the different effects of ionic strength on the different transport mechanism of DEAE-dextran modified resins and DEAE Sepharose FF.In addition,the De values of DEAE-dextran modified resins showed an increase-then-decrease trend with increasing protein initial concentration,and reached a maximum at 1 mg/m L BSA.The experimental results would benefit in the selection as well as the design of high-performance media for protein chromatography.Besides,the work will promote the development of protein adsorption theories of polymer-grafting resins and extend the application of polymer-grafting resins in industrial production of protein pharmaceuticals.