Native Chemical Ligation at Asx-Cys, Glx-Cys: Chemical Synthesis and High-Resolution X-ray Structure of ShK Toxin by Racemic Protein Crystallography

• DOI: 10.1021/ja4046795
• Publication Date: 2013-07-12T22:20:36Z
• Authors: Bobo Dang; Tomoya Kubota; Kalyaneswar Mandal; Francisco Bezanilla; Stephen B. H. Kent
• Keywords: Native chemical ligation; Chemical structure; Chemical Ligation; Chemical modification

We have re-examined the utility of native chemical ligation at -Gln/Glu-Cys- [Glx-Cys] and -Asn/Asp-Cys- [Asx-Cys] sites. Using improved thioaryl catalyst 4-mercaptophenylacetic acid (MPAA), could be performed -Gln-Cys- Asn-Cys- sites without side reactions. After optimization, a -Glu-Cys- site also used as site, with minimal levels byproduct formation. However, -Asp-Cys- is not appropriate for use because formation significant amounts β-linked byproduct. The feasibility enabled convergent total synthesis enantiomeric forms ShK toxin protein molecule. d-ShK molecule was ∼50,000-fold less active in blocking Kv1.3 channel than l-ShK Racemic crystallography to obtain high-resolution X-ray diffraction data toxin. structure solved by direct methods showed differences from previously reported NMR structures some regions