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-fluoroenylmethoxy-carbonyl (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.