Protein-maleimide Conjugates for Thiol-conjugate Addition

Malemides, a common structural feature found in biological systems are notably able to specifically react with free thiol (SH) groups under biological conditions in the pH range of 6.5–7.5 to form a stable thioether moiety¹⁾ (Figure 1).

Figure 1. Reaction of thiol compounds and maleimides

Thiol groups are typically present as side chains of cysteine residues in a protein. However, in case of proteins without cysteine residues, the thiol group can be introduced to primary amines by adding SATA or SATP. Furthermore, disulfide moieties in proteins can be disconnected by reductants such as DTT or MEA to reveal free thiols.
1, 2, and 3, three protein conjugates containing a thiol-reactive maleimide group can be used to conjugate to proteins and peptides containing free thiols. For example, 2 is utilized in the HRP-labelling of an antibody (Figure 2). Each protein conjugate are packaged for single use purposes and thus do not require massing prior to use.

Figure 2. HRP-labelling of an antibody with 2