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Native chemical ligation at Asx-Cys, Glx-Cys: chemical synthesis and high-resolution X-ray structure of ShK toxin by racemic protein crystallography.

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

SUBMITTER: Dang B

PROVIDER: S-EPMC3838204 | biostudies-literature | 2013 Aug

REPOSITORIES: biostudies-literature

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Native chemical ligation at Asx-Cys, Glx-Cys: chemical synthesis and high-resolution X-ray structure of ShK toxin by racemic protein crystallography.

Dang Bobo B Kubota Tomoya T Mandal Kalyaneswar K Bezanilla Francisco F Kent Stephen B H SB

Journal of the American Chemical Society 20130806 32

We have re-examined the utility of native chemical ligation at -Gln/Glu-Cys- [Glx-Cys] and -Asn/Asp-Cys- [Asx-Cys] sites. Using the improved thioaryl catalyst 4-mercaptophenylacetic acid (MPAA), native chemical ligation could be performed at -Gln-Cys- and Asn-Cys- sites without side reactions. After optimization, ligation at a -Glu-Cys- site could also be used as a ligation site, with minimal levels of byproduct formation. However, -Asp-Cys- is not appropriate for use as a site for native chemic ...[more]

PMID: 23919482

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Project description:Oxo-ester mediated native chemical ligation (OMNCL) is a variation of the more general native chemical ligation (NCL) reaction that is widely employed for chemoselective ligation of peptide fragments. While OMNCL has been used for a variety of peptide ligations and for biomolecular modification of surfaces, it is typically practiced under harsh conditions that are unsuitable for use in a biological context. In this report we describe the use of OMNCL for polymer hydrogel formation, in-vitro cell encapsulation, and in-vivo implantation. Multivalent polymer precursors containing N-hydroxysuccinimide (NHS) activated oxo-esters and N-cysteine (N-Cys) endgroups were chemically synthesized from branched poly(ethylene glycol) (PEG). Hydrogels formed rapidly at physiologic pH upon mixing of aqueous solutions of NHS and N-Cys functionalized PEGs. Quantitative 1H NMR experiments showed that the reaction proceeds through an OMNCL pathway involving thiol capture to form a thioester intermediate, followed by an S-to-N acyl rearrangement to yield an amide cross-link. pH and temperature were found to influence gelation rate, allowing tailoring of gelation times from a few seconds to a few minutes. OMNCL hydrogels initially swelled before contracting to reach an equilibrium increase in relative wet weight of 0%. This unique behavior impacted the gel stiffness and was attributed to latent formation of disulfide cross-links between network-bound Cys residues. OMNCL hydrogels were adhesive to hydrated tissue, generating a lap shear adhesion strength of 46 kPa. Cells encapsulated in OMNCL hydrogels maintained high viability, and in-situ formation of OMNCL hydrogel by subcutaneous injection in mice generated a minimal acute inflammatory response. OMNCL represents a promising strategy for chemical cross-linking of hydrogels in a biological context and is an attractive candidate for in-vivo applications such as wound healing, tissue repair, drug delivery, and tissue engineering.

Dataset Information

Native chemical ligation at Asx-Cys, Glx-Cys: chemical synthesis and high-resolution X-ray structure of ShK toxin by racemic protein crystallography.

Publications

Native chemical ligation at Asx-Cys, Glx-Cys: chemical synthesis and high-resolution X-ray structure of ShK toxin by racemic protein crystallography.

Similar Datasets

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