Liquid-liquid phase separation of a monoclonal antibody and nonmonotonic influence of Hofmeister anions.
Liquid-liquid phase separation was studied for a monoclonal antibody in the monovalent salt solutions of KF, KCl, and KSCN under different pH conditions. A modified Carnahan-Starling hard-sphere model was utilized to fit the experimental data, establish the liquid-liquid coexistence curve, and determine antibody-antibody interactions in the form of T(c) (critical temperature) under the different solution conditions. The liquid-liquid phase separation revealed the complex relationships between antibody-antibody interactions and different solution conditions, such as pH, ionic strength, and the type of anion. At pH 7.1, close to the pI of the antibody, a decrease of T(c) versus ionic strength was observed at low salt conditions, suggesting that the protein-protein interactions became less attractive. At a pH value below the pI of the antibody, a nonmonotonic relationship of T(c) versus ionic strength was apparent: initially as the ionic strength increased, protein-protein interactions became more attractive with the effectiveness of the anions following the inverse Hofmeister series; then the interactions became less attractive following the direct Hofmeister series. This nonmonotonic relationship may be explained by combining the charge neutralization by the anions, perhaps with the ion-correlation force for polarizable anions, and their preferential interactions with the antibody.
Department of Analytical and Formulation Sciences, Amgen, Thousand Oaks, California, USA.
Bruce D
BD
Mason
Jian
J
Zhang-van Enk
Le
L
Zhang
Richard L
RL
Remmele
Jifeng
J
Zhang
D000838:Anions / Q000737:chemistry*; D000911:Antibodies, Monoclonal / Q000737:chemistry* / Q000302:isolation & purification*; D005459:Fluorides / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007526:Isoelectric Point; D008956:Models, Chemical; D009994:Osmolar Concentration; D044367:Phase Transition; D011189:Potassium Chloride / Q000737:chemistry; D017680:Potassium Compounds / Q000737:chemistry; D013696:Temperature; D013861:Thiocyanates / Q000737:chemistry
D000838:Anions; D000911:Antibodies, Monoclonal; D017680:Potassium Compounds; D013861:Thiocyanates; D011189:Potassium Chloride; C033320:potassium fluoride; D005459:Fluorides; C009941:potassium thiocyanate