Affinity purification of synthetic peptides.

Abstract

A general strategy and a specific tactic for affinity purification of polypeptides synthesized on solid supports are described and demonstrated. The desired peptide chains were distinguished from terminated peptide chains before removal from the support by attachment of an affinity reagent (cysteinyl-methionine) bearing an affinity group (thiol) and a binding group (carboxylic acid). After cleavage from the synthetic support, the affinity-labeled peptides (Cys-Met-peptides) were bound to an affinity receptor (organomercurial-agarose) and thus separated from terminated peptides and all other peptides lacking the affinity group. The desired synthetic peptide was obtained by separation of the affinity-labeled peptides from the affinity receptor (displacement by cysteine or other thiol) followed by removal of the affinity reagent (loss of Cys-Met by cyanogen bromide cleavage). This general affinity purification strategy is independent of the length or amino acid sequence of the desired peptide. After assembly of RNase-(111-124)-tetradecapeptide, using radiolabeled acetic anhydride for termination of uncoupled intermediates, essentially all (> 98.5%) of the acetylated deletion peptides were removed by employing the organomercurial Cys-Met tactic. The purity of crude synthetic histone H4-(1-37)-heptatriacontapeptide was increased 6-fold by using this tactic to remove terminated peptides. A related dimeric Cys-Met tactic is outlined for affinity purification of peptides containing internal cysteine and methionine residues.