Application of docking methods for metal chelate affinity precipitation of endo-glucanase using pH-response polymer.

An endo-glucanase could be efficiently purified using metal chelate affinity precipitation by a pH-response polymer PMMDN with iminodiacetic acid (IDA) and Cu(2+) as affinity ligand. In this study, docking method was used to identify the appropriate chelator and the metal ion as ligand by Grid score. The simulation results were compared with the label-free detection data analyzed by ForteBio's Octet. The ligand IDA-Cu(2+) was the final choice. A pH-response polymer PMMDN was polymerized and subsequently coupled with IDA-Cu(2+)as the ligand. The pI and recovery of PMMDN and PMMDN-IDA-Cu(2+) were 4.50, 99.8% and 4.39, 97.6%, respectively. Optimal adsorption conditions were found to be ligand density of 3.0 mmol/g, pH 5.5 and 1.0 mol/L NaCl. The adsorption isotherm showed the maximum adsorption as 57.62 mg/g polymer and the dissociation constant as 1.08 mg/mL. For the elution of the PMMDN-IDA-Cu(2+) with the protein, 0.5 mol/L imidazole containing 1.0 mol/L guanidine hydrochloride was used as the eluent. Under these conditions, electrophoretic purity of endo-glucanase was obtained by only one step, and the elution recoveries were 96.45% (protein) and 93.24% (activity).