Synthesis and purification of hydrophobic peptides for use in biomimetic ion channels

Synthesis of an O-acyl isopeptide by using native chemical ligation in an aqueous solvent system

O-Acyl isopeptides, in which the N-acyl linkage on the hydroxyamino acid residue (e.g. Ser and Thr) is replaced by an O-acyl linkage, generally suppress unfavorable aggregation properties derived from the corresponding parent peptides. Here, we report the synthesis of an O-acyl isopeptide of 34-mer pyroGlu-ADan (2), a component of amyloid deposits in hereditary familial Danish dementia, by using native chemical ligation. Native chemical ligation of pyroGlu(1) -ADan(1-21)-SCH2 CH2 SO3 (-) Na(+) (3) and Cys(22) -O-acyl isopeptide (4), in which the amino group of the Ser(29) residue at the isopeptide moiety was protected by an allyloxycarbonyl group, proceeded well in an aqueous solvent to yield a ligated O-acyl isopeptide (5). Subsequent disulfide bond formation and deprotection of the allyloxycarbonyl group followed by HPLC purification gave 2 with a reasonable overall yield. 2 was converted to the parent peptide 1 via an O-to-N acyl migration reaction. The sequential method, namely (i) native chemical ligation of the O-acyl isopeptide, (ii) HPLC purification as the O-acyl isopeptide form, and (iii) O-to-N acyl migration into the desired polypeptide, would be helpful to solve problems with HPLC purification of hydrophobic polypeptides in the process of chemical protein synthesis.

Towards the total chemical synthesis of integral membrane proteins: a general method for the synthesis of hydrophobic peptide-thioester building blocks

Modification of a peptide-(α)thioester with a sequence of six arginines on the thioester leaving group can render soluble all peptides derived from a polytopic integral membrane protein. This strategy greatly simplifies the synthesis of peptide-(α)thioester building blocks for the total chemical synthesis of integral membrane proteins by native chemical ligation.

Separations of hydrophobic synthetic peptides in counter-current chromatography

Synthetic peptides with many aromatic, aliphatic and especially acidic amino acid residues are not very soluble and require strong solvents for useful partitioning. A chloroform-methanol-acidic solvent system fractionates neutral and basically charged 26-mers to provide high yields. An insoluble 15-mer with 5 Trp residues and 60% overall hydrophobic amino acid content was purified in pyridine-acetic acid and in another basic t-butyl methyl ether-n-butanol-acetonitrile solvent system with high recovery. Two instruments were used, the eccentric-multi-layer hybrid coil planet centrifuge and the new spiral disk planet centrifuge that were able to retain the stationary phase of these solvent systems, some of which have low interfacial tension.

Studies on the Insolubility of a Transmembrane Peptide from Signal Peptide Peptidase

We have undertaken fundamental studies on the solubility properties of a peptide derived from the fourth transmembrane (TM) domain of signal peptide peptidase, a 7-TM intramembrane-cleaving protease. We have found that by disfavoring secondary structure formation we are able to greatly improve the solubility, handling, and purification properties of this peptide. Our findings suggest that preventing secondary structure formation by reversible modification of the polypeptide backbone of hydrophobic transmembrane peptides may be a useful strategy for the total chemical protein synthesis of integral membrane proteins.