Acyl cystamine: small-molecular foldase mimics accelerating oxidative refolding of disulfide-containing proteins

β-Cyclodextrin-Modified Magnetic Nanoparticles Immobilized on Sepharose Surface Provide an Effective Matrix for Protein Refolding

In this article, we propose an impressive and facile strategy to improve protein refolding using solid phase artificial molecular chaperones consisting of the surface-functionalized magnetic nanoparticles. Specifically, monotosyl-β-cyclodextrin connected to the surface of 3-aminopropyltriethoxysilane (APES)-modified magnetic nanoparticles is immobilized on the sepharose surface to promote interaction with exposed hydrophobic surfaces of partially folded (intermediates) and unfolded states of proteins. Their efficiencies were investigated by circular dichroism spectroscopy and photoluminescence spectroscopy of the protein. Although the mechanism of this method is based on principles of hydrophobic chromatography, this system is not only purging the native protein from inactive inclusion bodies but also improving the protein refolding process. We chose β-cyclodextrin (β-CD) considering multiple reports in the literature about its efficiency in protein refolding and its biocompatibility. To increase the surface area/volume ratio of the sepharose surface by nanoparticles, more β-CD molecules are connected to the sepharose surface to make a better interaction with proteins. We suppose that proteins are isolated in the nanospace created by bound cyclodextrins on the resin surface so intermolecular interactions are reduced. The architecture of nanoparticles was characterized by Fourier transform infrared spectra, X-ray diffraction, scanning electron microscopy images, energy dispersive X-ray spectroscopy, nuclear magnetic resonance (¹H NMR and ¹³C NMR), and dynamic light scattering.

Protein disulfide isomerase as a novel target for cyclopentenone prostaglandins: implications for hypoxic ischemic injury

Cyclooxygenase-2 (COX-2) is an important contributor to ischemic brain injury. Identification of the downstream mediators of COX-2 toxicity may allow the development of targeted therapies. Of particular interest is the cyclopentenone family of prostaglandin metabolites. Cyclopentenone prostaglandins (CyPGs) are highly reactive molecules that form covalent bonds with cellular thiols. Protein disulfide isomerase (PDI) is an important molecule for the restoration of denatured proteins following ischemia. Because PDI has several thiols, including thiols within the active thioredoxin-like domain, we hypothesized that PDI is a target of CyPGs and that CyPG binding of PDI is detrimental. CyPG-PDI binding was detected in vitro via immunoprecipitation and MS. CyPG-PDI binding decreased PDI enzymatic activity in recombinant PDI treated with CyPG, and PDI immunoprecipitated from neuronal culture treated with CyPG or anoxia. Toxic effects of binding were demonstrated in experiments showing that: (a) pharmacologic inhibition of PDI increased cell death in anoxic neurons, (b) PDI overexpression protected neurons exposed to anoxia and SH-SY5Y cells exposed to CyPG, and (c) PDI overexpression in SH-SY5Y cells attenuated ubiquitination of proteins and decreased activation of pro-apoptotic caspases. In conclusion, CyPG production and subsequent binding of PDI is a novel and potentially important mechanism of ischemic brain injury. We show that CyPGs bind to PDI, cyclopentenones inhibit PDI activity, and CyPG-PDI binding is associated with increased neuronal susceptibility to anoxia. Additional studies are necessary to determine the relative role of CyPG-dependent inhibition of PDI activity in ischemia and other neurodegenerative disorders.

Organocatalysts of oxidative protein folding inspired by protein disulfide isomerase

Organocatalysts derived from diethylenetriamine effect the rapid isomerization of non-native protein disulfide bonds to native ones. These catalysts contain a pendant hydrophobic moiety to encourage interaction with the non-native state, and two thiol groups with low pKa values that form a disulfide bond with a high E°' value.