Prevention of Aggregation of Synthetic Membrane-Spanning Peptides by Addition of Detergent

Abstract

In our initial attempts to solubilize and purify a chemically synthesized 22-amino acid, membrane-spanning peptide, we encountered numerous difficulties. The peptide was not soluble in dilute acids, organic solvents, or chaotropic agents (±detergent) following standard HF cleavage protocols. The insolubility was a direct result of the formation of peptide-(peptide)_n aggregates that occurred during the initial phase of isolation, i.e., during the HF cleavage. Eliminating the ether precipitation and subsequent washes did not decrease the degree of aggregation of the product. Inclusion of nonionic detergents in the HF-cleavage reactions displayed little ability in preventing aggregation. Cleavage in the presence of sodium dodecyl sulfate, however, dramatically reduced the degree of aggregation, even after washing with organic solvents. The cleaved peptide was purified to homogeneity using a detergent-based HPLC protocol. This column procedure also permits the quantitative exchange of the sodium dodecyl sulfate for n-octyl-β-d-glucopyranoside. Combined use of the two protocols results in high-yield isolations for a class of peptides that is generally difficult to handle.