Phosphorylation as Conformational Switch from the Native to Amyloid State - Trp-Cage as Protein Aggregation Model

Kardos, József and Kiss, Bence and Micsonai, András and Rovó, Petra and Kovács, János and Váradi, Györgyi and Tóth, Gábor K. and Perczel, András (2014) Phosphorylation as Conformational Switch from the Native to Amyloid State - Trp-Cage as Protein Aggregation Model. Journal of Physical Chemistry B. ISSN 1520-6106, ESSN: 1520-5207 (Unpublished)

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Abstract

The 20 residue long Trp-cage miniprotein is an excellent model both for computational and experimental studies of protein folding and stability. Recently, a great attention emerged to study disease-related protein misfolding, aggregation and amyloid formation, with the aim of revealing their structural and thermodynamic background. Trp-cage is sensitive to both environmental and structure-modifying effects, and aggregates with ease upon structure destabilization and thus, it is an ideal model of aggregation and amyloid formation. Here, we characterize the amyloid formation of several sequence modified and side-chain phosphorylated Trp-cage variants. We applied NMR, CD, FTIR spectroscopy, transmission electron microscopy in conjunction with thioflavin-T fluorescence measurements to reveal the structural consequences of the side-chain phosphorylation. We demonstrate that the native fold is destabilized upon serine phosphorylation and the resultant highly dynamic structures form amyloid-like ordered aggregates with high intermolecular β-structure content. The only exception is the D9S(P) variant which follows an alternative aggregation process by forming thin fibrils, presenting a CD spectrum of PPII helix, and showing low ThT binding capability. We propose a complex aggregation model for these Trp-cage miniproteins. This model assumes an additional aggregated state, a collagen triple helical form which can precede amyloid formation. The phosphorylation of a single serine residue serves as a conformational switch, triggering aggregation, otherwise mediated by kinases in cell. We show that Trp-cage miniprotein is indeed a realistic model of larger globular systems of composite folding and aggregation landscapes and helps us to understand the fundamentals of deleterious protein aggregation and amyloid formation.

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