RESUMEN
The application of solid-phase peptide synthesis and native chemical ligation in chemical protein synthesis (CPS) has enabled access to synthetic proteins that cannot be produced recombinantly, such as site-specific post-translationally modified or mirror-image proteins (D-proteins). However, CPS is commonly hampered by aggregation and insolubility of peptide segments and assembly intermediates. Installation of a solubilizing tag consisting of basic Lys or Arg amino acids can overcome these issues. Through the introduction of a traceless cleavable linker, the solubilizing tag can be selectively removed to generate native peptide. Here we describe the synthesis of a next-generation amine-reactive linker N-Fmoc-2-(7-amino-1-hydroxyheptylidene)-5,5-dimethylcyclohexane-1,3-dione (Fmoc-Ddap-OH) that can be used to selectively introduce semi-permanent solubilizing tags ("helping hands") onto Lys side chains of difficult peptides. This linker has improved stability compared to its predecessor, a property that can increase yields for multi-step syntheses with longer handling times. We also introduce a new linker cleavage protocol using hydroxylamine that greatly accelerates removal of the linker. The utility of this linker in CPS was demonstrated by the preparation of the synthetically challenging Shiga toxin subunit B (StxB) protein. This robust and easy-to-use linker is a valuable addition to the CPS toolbox for the production of challenging synthetic proteins.
Asunto(s)
Péptidos/química , Subunidades de Proteína/síntesis química , Toxina Shiga/síntesis química , Técnicas de Síntesis en Fase Sólida/métodos , Secuencia de Aminoácidos , Arginina/química , Ciclohexanonas/química , Hidroxilamina/química , Lisina/química , SolubilidadRESUMEN
Shiga toxins are one of the very potent agents for causing dysentery, diarrhoea and haemolytic uremic syndrome with very low LD50. For better understanding of their biology, detection and neutralization, the components of toxins are needed to be expressed and purified in bulk amounts. However, following traditional expression procedures, this task is very tedious as the yield of the toxin is very low. In this manuscript, we have described the optimization of media for enhanced production of recombinant Shiga toxin B (rStx-B) chain protein in Escherichia coli. This protein is known to have neutralization ability against shiga toxins. Furthermore, fed-batch cultivation process in E. coli was also developed in the optimized medium. Expression was induced with 1 mM isopropyl-beta-thiogalactoside (IPTG). The purification of protein involved Ni-NTA affinity chromatography under native conditions followed by gel filtration chromatography. After fed-batch cultivation, the recombinant E. coli resulted in cell weight and purified protein of about 19.41 g/l (dry cell weight, 11.38 g/l) and 30 mg/l of culture, respectively. The purity of the recombinant StxB protein was checked by sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis. Reactivity of this protein was determined by Western blotting as well as indirect ELISA using specific antibodies. These results establish the application of this protein for diagnosis of shiga toxin infection or for neutralizing the toxicity.