Stereospecific interactions between histidine and monoclonal antibodies.

Histidine is a frequently used buffer in the final formulation of many commercialized monoclonal antibodies (mAbs), with histidine helping to stabilize the antibody during storage in addition to its buffering function. The objective of this study was to examine the stereospecificity of any histidine-antibody interactions using a combination of experimental studies and molecular dynamics simulations. Isothermal titration calorimetry provided evidence of weak stereospecific interactions, with the antibody showing approximately two to four additional interaction sites for d- versus l-histidine. The greater interactions with d-histidine were confirmed by measurements of the net protein charge using electrophoretic light scattering. The reduction in the net negative charge of the antibody in d-histidine led to significantly different behavior during diafiltration due to Donnan exclusion effects. Molecular dynamics simulations corroborated the presence of additional d-histidine interaction sites. These results provide the first demonstration of weak stereospecific interactions between l- and d-histidine and a mAb and the implications of these interactions for antibody formulation.