Ricin A chain insertion into endoplasmic reticulum membranes is triggered by a temperature increase to 37 {degrees}C.

After endocytic uptake by mammalian cells, the heterodimeric plant toxin ricin is transported to the endoplasmic reticulum (ER), where the ricin A chain (RTA) must cross the ER membrane to reach its ribosomal substrates. Here, using gel filtration chromatography, sedimentation, fluorescence, fluorescence resonance energy transfer, and circular dichroism, we show that both fluorescently labeled and unlabeled RTA bind both to ER microsomal membranes and to negatively charged liposomes. The binding of RTA to the membrane at 0-30 degrees C exposes certain RTA residues to the nonpolar lipid core of the bilayer with little change in the secondary structure of the protein.

A screening system for the identification of refolding conditions for a model protein kinase, p38alpha.

Protein kinases are key drug targets involved in the regulation of a wide variety of cellular processes. To aid the development of drugs targeting these kinases, it is necessary to express recombinant protein in large amounts. The expression of these kinases in Escherichia coli often leads to the accumulation of the expressed protein as insoluble inclusion bodies.