Fmoc-based synthesis of the human CC chemokine CCL14/HCC-1 by SPPS and native chemical ligation

Abstract

The CC chemokine CCL14/HCC-1(9-74), a 66-residue polypeptide containing two disulfide bonds, was recently discovered from a human hemofiltrate peptide library as a high-affinity ligand of the chemokine receptors CCR1 and CCR5. It has been shown to inhibit HIV infection by blocking CCR5. Using Fmoc methodology, we report the chemical synthesis of CCL14/HCC-1 by conventional stepwise solid-phase peptide synthesis (SPPS) and, alternatively, native chemical ligation. To optimize SPPS of CCL14/HCC-1, difficult sequence regions were identified by mass spectrometry, in order to obtain a crude tetrathiol precursor suitable for oxidative disulfide formation. For synthesis of CCL14/HCC-1 by native chemical ligation, the peptide was divided into two segments, CCL14/HCC-1(9-39) and CCL14/HCC-1(40-74), the latter containing a cysteine residue at the amino-terminus. The synthesis of the thioester segment was carried out comparing a thiol linker with a sulfonamide safety-catch linker. While the use of the thiol linker led to very low overall yields of the desired thioester, the sulfonamide linker was efficient in obtaining the 31-residue thioester of CCL14/HCC-1(9-39), suggesting a superior suitability of this linker in generating larger thioesters using Fmoc chemistry. The thioester of CCL14/HCC-1 was subsequently ligated with the cysteinyl segment to the full-length chemokine. Disulfides were introduced in the presence of the redox buffer cysteine/cystine. The products of both SPPS and native chemical ligation were identical. The use of a sulfonamide safety-catch linker enables the Fmoc synthesis of larger peptide thioesters, and is thus useful to generate arrays of larger polypeptides.