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Folding and stability of the leucine-rich repeat domain of internalin B from Listeria monocytogenes
(2004)
Internalin B (InlB), a surface protein of the human pathogen Listeria monocytogenes, promotes invasion into various host cell types by inducing phagocytosis of the entire bacterium. The N-terminal half of InlB (residues 36-321, InlB(321)), which is sufficient for this process, contains a central leucine-rich repeat (LRR) domain that is flanked by a small a-helical cap 2 and an immunoglobulin (Ig)-like domain. Here we investigated the variant lacking the Ig-like domain (lnlB(248)). The circular dichroism spectra of both protein variants in the far ultraviolet region are very similar, with a characteristic minimum found at similar to200 nm, possibly resulting from the high 3(10)-helical content in the LRR domain. Upon addition of chemical denaturants, both variants unfold in single transitions with unusually high cooperativity that are fully reversible and best described by two-state equilibria. The free energies of GdmCl-induced unfolding determined from transitions at 20degreesC are 9.9(+/- 0.8)kcal/mol for InlB(321) and 5.4(+/- 0.4) kcal/mol for InlB(248). InlB(321) is also more stable against thermal denaturation, as observed by scanning calorimetry. This suggests, that the Ig-like domain, which presumably does not directly interact with the host cell receptor during bacterial invasion, plays a critical role for the in vivo stability of InlB. (C) 2004 Elsevier Ltd. All rights reserved
The preparation of proteins for structural and functional analysis using the Escherichia coli expression system is often hampered by the formation of insoluble intracellular protein aggregates (inclusion bodies). Transferring those proteins into their native states by in vitro protein folding requires screening for the best buffer conditions and suitable additives. However, it is difficult to assess the success of such a screen if no biological assay is available. We established a fully automated folding screen and a system to detect folded protein that is based on analytical hydrophobic interaction chromatography and tryptophan fluorescence spectroscopy. The system was evaluated with two model enzymes (carbonic anhydrase II and malate dehydrogenase), and was successfully applied to the folding of the p22 subunit of human dynactin, which is expressed in inclusion bodies in E. coli. The described screen allows for high-throughput folding analysis of inclusion body proteins for structural and functional analyses