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Probing the Residual Structure in Avian Prion Hexarepeats by CD, NMR and MD Techniques
Dipartimento di Scienze e Tecnologie Ambientali, Biologiche e Farmaceutiche, Seconda Università di Napoli, via Vivaldi 43, 81100 Caserta, Italy
CNR-Istituto di Biostrutture e Bioimmagini, viale Doria 6, 95125 Catania, Italy
Centro Interuniversitario di Ricerca sui Peptidi Bioattivi, Università di Napoli "Federico II", Via Mezzocannone 16, 80134 Napoli, Italy
Dipartimento di Farmacia, Università di Pisa, Via Bonanno Pisano 6, 56126 Pisa, Italy
* Author to whom correspondence should be addressed.
Received: 5 August 2013; in revised form: 3 September 2013 / Accepted: 9 September 2013 / Published: 16 September 2013
Abstract: Many proteins perform essential biological functions by means of regions that lacking specific organized structure exist as an ensemble of interconverting transient conformers. The characterization of such regions, including the description of their structural propensities, number of conformations and relative populations can provide useful insights. Prion diseases result from the conversion of a normal glycoprotein into a misfolded pathogenic isoform. The structures of mammal and chicken prion proteins show a similar fold with a globular domain and a flexible N-terminal portion that contains different repeated regions: octarepeats (PHGGGWGQ) in mammals and hexarepeats (PHNPGY) in chickens. The higher number of prolines in the hexarepeat region suggests that this region may retain a significant amount of residual secondary structure. Here, we report the CD, NMR and MD characterization of a peptide (2-HexaPY) composed of two hexarepeats. We combine experimental NMR data and MD to investigate at atomic level its ensemble-averaged structural properties, demonstrating how each residue of both repeats has a different quantified PPII propensity that shows a periodicity along the sequence. This feature explains the absence of cooperativity to stabilize a PPII conformation. Nonetheless, such residual structure can play a role in nucleating local structural transitions as well as modulating intra-molecular or inter-molecular interactions.
Keywords: avian prion repeats; NMR; CD; conformational ensemble; polyproline II
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Russo, L.; Raiola, L.; Campitiello, M.A.; Magrì, A.; Fattorusso, R.; Malgieri, G.; Pappalardo, G.; La Mendola, D.; Isernia, C. Probing the Residual Structure in Avian Prion Hexarepeats by CD, NMR and MD Techniques. Molecules 2013, 18, 11467-11484.
Russo L, Raiola L, Campitiello MA, Magrì A, Fattorusso R, Malgieri G, Pappalardo G, La Mendola D, Isernia C. Probing the Residual Structure in Avian Prion Hexarepeats by CD, NMR and MD Techniques. Molecules. 2013; 18(9):11467-11484.
Russo, Luigi; Raiola, Luca; Campitiello, Maria A.; Magrì, Antonio; Fattorusso, Roberto; Malgieri, Gaetano; Pappalardo, Giuseppe; La Mendola, Diego; Isernia, Carla. 2013. "Probing the Residual Structure in Avian Prion Hexarepeats by CD, NMR and MD Techniques." Molecules 18, no. 9: 11467-11484.