Journal
PROTEIN ENGINEERING DESIGN & SELECTION
Volume 26, Issue 4, Pages 255-265Publisher
OXFORD UNIV PRESS
DOI: 10.1093/protein/gzs102
Keywords
conformational stability; directed evolution; IgG1-Fc; protein aggregation; yeast surface display
Funding
- Christian Doppler Research Association
- Austrian Science Foundation FWF (PhD program BioToP - Biomolecular Technology of Proteins) [W1224]
- company F-star
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An Fcab (Fc antigen binding) is a crystallizable fragment of IgG having C-terminal structural loops of CH3 domains engineered for antigen binding. Since introduction of novel binding sites might impair the immunoglobulin fold, repairing strategies are needed for improving the biophysical properties of promising binders without decreasing affinity to the antigen. Here, a directed evolution protocol was developed and applied for stabilization of a Her2/neu-binding Fcab. Distinct loop regions of the parental binder were softly randomized by parsimonious mutagenesis, followed by heat incubation of the yeast displayed protein library and selection for retained antigen binding. Selected Fcabs were expressed solubly in Pichia pastoris and human embryonic kidney 293 cells and characterized. Fcab clones that retained their affinity to Her2/neu but exhibited a significantly increased conformational stability and resistance to aggregation could be evolved. Moreover, we demonstrate that simultaneous selection for binding to the antigen and to structurally specific ligands (FcRI and an antibody directed against the CH2 domain) yields even more stable Fcabs. To sum up, this study presents a very potent and generally applicable method for improving the fold and stability of antibodies, antibody fragments and alternative binding scaffolds.
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