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Protein Labeling and Conjugation

The most common functional groups targeted for protein bioconjugation include hydroxyl groups (found on Thr, Ser, and the phenolic group in Tyr), carboxylic acids (at the C-terminus and on Asp and Glu), sulfhydryls (on Cys), and amines (at the N-terminus and on Lys). Histidine's imidazolyl nitrogen and arginine's guanidinyl groups can also be modified, though they are less frequently used.

Because most proteins contain multiple copies of these same amino acids, conjugation methods using native functional groups often produce heterogeneous bioconjugates. To achieve site-specific labling, an orthogonal functional group must be introduced. The most widely used strategy is cysteine incorporation through mutagenesis. At CellMosaic, we specialize in working with Cys-mutant proteins and labeling them with a variety of molecules.

If the protein is glycosylated, another site-specific approach is glycan-based labeling. Adjacent hydroxyl groups on the carbohydrate moiety can be oxidized to form reactive formyl groups. CellMosaic offers a range of custom linkers and reagents designed to react specifically with these formyl groups under very mild conditions.

A less controlled method for generating more homogeneous protein conjugates involves optimizing reaction conditions in combination with effective purification strategies.

• Labeled protein reagents—please click here.
• PerKit® for protein labeling and conjugation—please click here.
• For large scale or project beyond the scope of PerKit™ configuration or our routine synthesis, please contact us for a quote.

Example 1: Synthesis of protein-KLH conjugates at CellMosaic (loaded 25 proteins per KLH).  

Example 2: Fluorescent labeling of a protein with defined DOL at CellMosaic (over 97.5% pure by SEC-HPLC, comprehensive bioanalytical tools were used to characterize the product).