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What methods do you recommend to conjugate a peptide to a carrier molecule?

The most important factor is that the site of conjugation be not an internal amino acid and that the site of conjugation be specific for a single amino acid. Internal amino acids and multiple conjugation sites will not present the peptide in a way that is most similar to the natural antigen. After that the choice of chemistry will be dependent on the type of amino acids present in the sequence.

Chemistry Site of reaction Not in the presence of Comments
Glutaraldehyde N-terminal NH2 group Lys (K) or an acetylated N-terminus or a Pro(P) N-terminus Not useful for peptides that correspond to the N-terminus of the antigen
EDCI C-terminal COOH group Glu (E), Asp (D) or an amidated C-terminus Not useful for peptides that correspond to the C-terminus of the antigen
MAP-8 C-terminal COOH group - Lower antigenicity than coupling to a carrier protein
BDB Terminal tyrosine Another Tyr (Y), Lys (K), Cys (C), His (H) Limited utility
MBS Side chain thiol of cysteine Another Cysteine (C) Commonly used approach, usually via the addition of an extra Cys (C) to the sequence at either the N- or C-terminus