You need to conjugate it to a carrier protein. Most people use KLH. If your peptide has no cys residues, the easiest approach is to add a cys at the end (either terminus) and use the thiol group for conjugation (i.e. to maleimide-KLH).

If you have already synthesized the peptide without terminal cys, then it would be useful to know the sequence to give best advice on conjugation to a carrier. There are several methods.

Nick Gee, Thank u for the response.

I have already got my peptide synthesised but it lacks cysteine residue.

It has Phenylalanine at the C-terminus and Tryptophan at the N-terminal.

Now, I'm not sure what carrier protein could be used for conjugation?

Before I answer do you have lys or asp/glu, and in which position(s). Regardless of the conjugation method, you would use KLH normally, and screen the sera against the peptide on a different protein, usually BSA. However, you can screen directly against the peptide too.

Nick Gee,

My peptide has

W(tryptophan) at the N-terminal, Serine at second position, Asp at 3,6 and 7 position. It lacks lysine and glu.

"WSDPGDD"

Nick is right. You should have included an Nter Cys for conjugation.

But as you have no competing amino moieties, (no Lys) you can try carbodiimide chemistry to couple to KLH through Nter. You'll activate the KLH with limiting CDI then add peptide. Look for recipes in The Protein Protocols Handbook.

Okay thanks. It is usual to conjugate to one of the terminal amino acid side chains, but in your case the residues are not favorable. Multiple carboxyl groups rules our carbodiimides (assuming you want a single point of attachment and no polymerization). However, the good news is that there are no lysines, which means you have a single amine at the N-terminus (assuming that your peptide was not N-terminally blocked). Therefore, your best approach with this peptide is probably glutaraldehyde conjugation.

You could still use a thiol-maleimide strategy which I think is much cleaner but from your current position you would need an extra step. i.e. to convert the N-terminal amine into a thiol.

I hope this helps.

Yes, John gives an useful additional option, if you adopt a TWO-step approach carbodiimides are not precluded.

@Nick is right. You can add an Nter thiol. Or you can do a 2-step CDI reaction.

Or you can try glutaraldehyde, which usually works but is non-reproducible. If you do try GluCHO, I recommend you try a 1-step "roar and pour" method. There's a 2-step method for that reagent, too, but it's finicky.

Thanks to Nick and Johh for the useful tips which I entirely agree with.

Ritu Narwal, I hope you find those suggestions helpful. Good luck.