The phase behavior study of human antibody solution using multi-scale modeling

Area of Science:

• Biophysics
• Materials Science
• Computational Chemistry

Background:

• Antibody solutions are of significant interest in academia and the pharmaceutical industry for their phase transformation properties.
• While spherical proteins exhibit liquid-liquid phase separation (LLPS), Y-shaped antibodies display unique phase diagrams distinct from spherical counterparts.

Purpose of the Study:

• To investigate the phase behavior of antibody solutions using molecular dynamics simulations.
• To compare simulation results with experimental data for human immunoglobulin G (IgG) to understand unique Y-shaped antibody phase diagrams.

Main Methods:

• Employed molecular dynamics simulations on trimetric Y-shaped coarse-grained models of antibodies.
• Developed a seven-site model with empirical parameters for exclusion volume and hinge length, fitted to experimental IgG data.

Main Results:

• Simulations successfully reproduced the experimentally observed low critical volume fraction (CVF) and asymmetric coexistence curve for IgG antibodies.
• Anisotropic inter-protein interactions and repulsion between inner spherical domains were identified as key factors influencing the broad and asymmetric phase diagram.
• Hinge length showed a minimal impact on CVF and the overall shape of the coexistence curve.

Conclusions:

• The Y-shape of antibodies leads to unique phase behavior, characterized by a low CVF and asymmetric liquid-liquid coexistence curve.
• Anisotropic interactions and specific structural features, like inner-domain repulsion, are crucial for understanding antibody phase diagrams.
• The developed seven-site model provides a foundation for further simulation studies on the phase behavior of IgG and similar Y-shaped molecules.