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Purification and characterization of recombinant N-terminally pyroglutamate-modified amyloid-beta variants and structural analysis by solution NMR spectroscopy

: Dammers, Christina; Gremer, Lothar; Neudecker, Philipp; Demuth, Hans-Ulrich; Schwarten, Melanie; Willbold, Dieter

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PLoS one. Online journal 10 (2015), No.10, Art. e0139710
ISSN: 1932-6203
Journal Article, Electronic Publication
Fraunhofer IZI ()

Alzheimer's disease (AD) is the leading cause of dementia in the elderly and is characterized by memory loss and cognitive decline. Pathological hallmark of AD brains are intracellular neurofibrillary tangles and extracellular amyloid plaques. The major component of these plaques is the highly heterogeneous amyloid-beta (A beta) peptide, varying in length and modification. In recent years pyroglutamate-modified amyloid-beta (pEA beta) peptides have increasingly moved into the focus since they have been described to be the predominant species of all N-terminally truncated A beta. Compared to unmodified A beta, pEA beta is known to show increased hydrophobicity, higher toxicity, faster aggregation and beta-sheet stabilization and is more resistant to degradation. Nuclear magnetic resonance (NMR) spectroscopy is a particularly powerful method to investigate the conformations of pEA beta isoforms in solution and to study peptide/ligand interactions for drug development. However, biophysical characterization of pEA beta and comparison to its non-modified variant has so far been seriously hampered by the lack of highly pure recombinant and isotope-enriched protein. Here we present, to our knowledge, for the first time a reproducible protocol for the production of pEA beta from a recombinant precursor expressed in E. coli in natural isotope abundance as well as in uniformly [U-N-15]-or [U-C-13, N-15]-labeled form, with yields of up to 15 mg/l E. coli culture broth. The chemical state of the purified protein was evaluated by RP-HPLC and formation of pyroglutamate was verified by mass spectroscopy. The recombinant pyroglutamate-modified A beta peptides showed characteristic sigmoidal aggregation kinetics as monitored by thioflavin-T assays. The quality and quantity of produced pEA beta 40 and pEA beta 42 allowed us to perform heteronuclear multidimensional NMR spectroscopy in solution and to sequence-specifically assign the backbone resonances under near-physiological conditions. Our results suggest that the presented method will be useful in obtaining cost-effective high-quality recombinant pEA beta 40 and pEA beta 42 for further physiological and biochemical studies.