Active site peptides with CXXC motif on map-resin can mimic protein disulfide isomerase activity

Two conserved Trp-Cys-Gly-His-Cys (WCGHC) sequences are assigned to act as catalytic sites for protein disulfide isomerase. Peptides containing the active site sequence, Ala-Pro-Trp-Cys-Gly-His-Cys-Lys(APWCGHCK), were synthesized both in a mono-molecular form and on multiple antigen peptide (MAP) resin or Wang resin by the 9-fluoroenylmethoxycarbonyl (Fmoc)-based solid-phase method. With scrambled RNase as a substrate, the (APWCGHCK)8-MAP was first shown to mimic the PDI activity, which was one thousandth of that of bovine PDI and comparable to that of thioredoxin. APWCGPCK and APWCGHCK, however, did not display a disulfide isomerase activity even at a concentration 8 times higher than that of (APWCGHCK)8-MAP. It was assumed that a sterically proper proximity of at least two active site peptides with CXXC motif was required for the expression of PDI activity.