Fc Engineering: Tailored Synthetic Human IgG1-Fc Repertoire for High-Affinity Interaction with FcRn at pH 6.0

Abstract

The therapeutic efficacy of an antibody drug depends on the variable domains and on the constant crystallizable fragment (Fc). IgG variable domains have been the targets of extensive molecular engineering in search of more specific binders with higher affinities for their targets. Similarly, Fc engineering approaches have led to modulating both the immune effector responses and serum half-lives of therapeutic antibodies. A high-affinity interaction between the IgG Fc and neonatal Fc receptor (FcRn) at a slightly acidic pH can protect IgG molecules from undergoing lysosomal or serum proteinase-induced degradation. Here we describe an optimized protocol for the development of a tailored, synthetic human Fc repertoire to select Fc mutants which show highly pH-restricted FcRn binding with high affinity.

Human IgG1 Fc pH-dependent optimization from a constant pH molecular dynamics simulation analysis

“…The overall stoichiometry arrangement of Fc-FcRn complexes was found to be similar in both rodents and humans, 8,10,11 where studies revealed the involvement of the FcRn a1-a2 domain platform interacting with the Fc CH 2 -CH 3 domain interface loops. Engineering studies on IgG1 for FcRn have also been reported, [12][13][14][15][16][17][18] with one of the most noteworthy Fc variant, the IgG1 Fc YTE mutant (Met252Tyr, Ser254Thr and Thr256Glu mutations). The IgG1 Fc YTE mutant was reported to show $10-fold improved pH-dependent binding affinity whilst exhibiting $2 to 4-fold prolonged serum half-life in humans.…”

“…14 Oen, the effects of the solvent environment such as pH are key factors in biochemical reactions, including the Fc-FcRn binding mechanism. 5,11,15,19 Although conventional molecular dynamics (MD) simulation has prompted molecular discovery in biological studies, system settings with a xed protonation state for solute titratable residues throughout the simulation may hinder the visualization of complex conformational changes in different pH environments. Thus, an auxiliary for MD simulation, constant pH molecular dynamics (CpHMD) simulation, which allows dynamic changes in the protonation states of titratable residues based on changes in the environmental pH was applied in this study.…”