Exploration of the Misfolding Mechanism of Transthyretin Monomer: Insights from Hybrid-Resolution Simulations and Markov State Model Analysis.

Shuangyan Zhou,Wenying Zhang,Mingyue Ma,Yusheng Dou,Glenn V Lo,Jie Cheng,Ting Yang,Shuai Yuan

doi:10.3390/biom9120889

Abstract

Misfolding and aggregation of transthyretin (TTR) is widely known to be responsible for a progressive systemic disorder called amyloid transthyretin (ATTR) amyloidosis. Studies suggest that TTR aggregation is initiated by a rate-limiting dissociation of the homo-tetramer into its monomers, which can rapidly misfold and self-assemble into amyloid fibril. Thus, exploring conformational change involved in TTR monomer misfolding is of vital importance for understanding the pathogenesis of ATTR amyloidosis. In this work, microsecond timescale hybrid-resolution molecular dynamics (MD) simulations combined with Markov state model (MSM) analysis were performed to investigate the misfolding mechanism of the TTR monomer. The results indicate that a macrostate with partially unfolded conformations may serve as the misfolded state of the TTR monomer. This misfolded state was extremely stable with a very large equilibrium probability of about 85.28%. With secondary structure analysis, we found the DAGH sheet in this state to be significantly destroyed. The CBEF sheet was relatively stable and sheet structure was maintained. However, the F-strand in this sheet was likely to move away from E-strand and reform a new β-sheet with the H-strand. This observation is consistent with experimental finding that F and H strands in the outer edge drive the misfolding of TTR. Finally, transition pathways from a near native state to this misfolded macrostate showed that the conformational transition can occur either through a native-like β-sheet intermediates or through partially unfolded intermediates, while the later appears to be the main pathway. As a whole, we identified a potential misfolded state of the TTR monomer and elucidated the misfolding pathway for its conformational transition. This work can provide a valuable theoretical basis for understanding of TTR aggregation and the pathogenesis of ATTR amyloidosis at the atomic level.

Highlights

Transthyretin (TTR) is a globular protein whose misfolding and amyloid aggregation is related to amyloid transthyretin (ATTR) amyloidosis that consists of wild-type ATTR (ATTRwt) amyloidosis and variant ATTR (ATTRv) amyloidosis [1]
Little is known about the pathogenesis of ATTR amyloidosis, which largelycontributes to the lack of clarity about the misfolding and aggregation mechanism of TTR
We explored the potential misfolding mechanism of the TTR monomer by combining microsecond hybrid-resolution molecular dynamics (MD) simulations and Markov state model (MSM) analysis

Summary

Introduction

Transthyretin (TTR) is a globular protein whose misfolding and amyloid aggregation is related to amyloid transthyretin (ATTR) amyloidosis that consists of wild-type ATTR (ATTRwt) amyloidosis and variant ATTR (ATTRv) amyloidosis [1]. A common pathological feature of different ATTR amyloidosis is the deposition of TTR amyloid fibril in various tissues, which causes significant damage to related organs [5,6]. Little is known about the pathogenesis of ATTR amyloidosis, which largelycontributes to the lack of clarity about the misfolding and aggregation mechanism of TTR. Once the TTR tetramer is dissociated into monomers, misfolding rapidly occurs and leads to aggregation into amyloid fibrils. It is critical to explore the misfolding mechanism of the TTR monomer, as it may provide significant clues for understanding the pathogenesis of ATTR amyloidosis

Methods

Results

Conclusion