Retention of modified BSA by ultrafiltration membranes

BACKGROUND: The efficiency of protein purification depends on membrane pore size and electrostatic repulsion between a protein and membrane surface. The current study investigates how deliberate protein modification affects the electrostatic repulsion, degree of protein separation and transmembrane flux. RESULTS: The experiments were performed with bovine serum albumin (BSA) modified by guanidation, succinylation and citraconation. The latter modification is reversible and can be used to improve the protein separation. Modified and native proteins were filtrated through polyethersulphone PES-20 membrane in dead-end and cross-flow filtration modes at pH 5-10. Guanidation diminished electronegativity of the protein. In dead-end mode, the relative flux in separation of modified BSA decreased to 0.45-0.7 of the flux of pure water over 27.5min. In the case of unmodified BSA, the average relative flux drop was 0.3-0.5. The separation of guanidated BSA increased on average by 11% in acidic conditions. Succinylation and citraconation increased BSA electronegativity. The average flux remained close to the flux of pure water declining by 0.2-0.4, and the separation was greater than 95% at alkaline conditions in both dead-end and cross-flow operational modes. CONCLUSION: Suggested modifications do not require changes in chemistry of bulk suspensions and membranes, but do increase protein rejection keeping high transmembrane flux. The suggested approach is novel and holds the promise of achieving the purity level of therapeutic proteins required by drug authorities. Under the conditions investigated the best results were observed for succinylation and filtration in cross-flow mode at pH 5-10.