![]() ![]() Yeast surface display has become a powerful protein engineering tool, with broad applications including antibody affinity improvement, binding epitope mapping, enzyme engineering, and others ( Cherf and Cochran 2015, Mei, Zhou et al. Incorporation of a covalent SNAP tag thus overcomes disadvantages of conventional antibody-based expression tags and enables protein-engineering applications outside of physiological pH. Our results demonstrated that covalent SNAP tags can effectively quantify protein-surface expression at low pH, enabling the enrichment of Fc variants with increased affinity at pH 6.0 to the neonatal Fc receptor (FcRn). We compared the SNAP tag to conventional antibody-based peptide fusion and to direct fluorescent domain fusion using antibody fragment crystallizable (Fc) gene libraries as a case study in low pH protein engineering. SNAP forms a covalent bond with its small-molecule substrate, enabling precise and pH-independent protein display tagging. ![]() In this study, a SNAP tag was introduced to a yeast display platform to circumvent disadvantages of conventional antibody display tags at low pH. However, antibody-antigen interactions require high stability for accurate quantification, and conventional tag systems based on such interactions may not be compatible with a low pH environment. Antibody-based peptide interactions are often used to quantify yeast surface expression (e.g., by fusing a target protein to a FLAG, Myc, polyhistidine, or other peptide tag). Yeast display has become an important tool for modern biotechnology with many advantages for eukaryotic protein engineering.
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