Structure-Based Analysis of A19D, a Variant of Transthyretin Involved in Familial Amyloid Cardiomyopathy

Abstract

Transthyretin (TTR) is a tetrameric beta-sheet-rich protein. Its deposits have been implicated in four different amyloid diseases. Although aggregation of the wild-type sequence is responsible for the senile form of the disease, more than one hundred variants have been described thus far, most of which confer a more amyloidogenic character to TTR, mainly because they compromise the stability of the protein in relation to monomer formation, which upon misfolding is intrinsically aggregation-prone. We report the case of a Brazilian patient suffering from a severe cardiomyopathy who carries a rare mutation in exon 2 of the TTR gene that results in an Ala to Asp substitution at position 19 (A19D). The putative pathogenic mechanisms of this variant were analyzed in silico. We constructed a structural model for the A19D tetramer from which its thermodynamic stability was compared to that displayed by the V30M (more amyloidogenic than WT-TTR) and T119M (non-amyloidogenic) variants. The FoldX force field predicted that A19D and V30M are 10.88 and 8.07 kCal/mol less stable than the WT-TTR, while T119M is 5.15 kCal/mol more stable, which is consistent with the aggregation propensities exhibited by these variants. We analyzed the step in which the tetramer-dimer-monomer-unfolded monomer equilibrium might contribute the most to the increased or decreased amyloidogenicity in each variant. Our results suggest that the concentration of four non-native negative charges occur inside thyroxine-binding channels, and the loss of contacts at both the tetrameric and dimeric interfaces would account for an overall decreased stability of the tetramer and the consequent enhanced amyloidogenicity of the A19D variant. As far as we know, this is the first description of a non-V30M mutation in Brazil.

Fluorotryptophan Incorporation Modulates the Structure and Stability of Transthyretin in a Site-Specific Manner

“…The AB loop, which forms part of the weak dimer interface, contains pathogenic variants of D18G, A19D, V20I, S23N, P24S A25T and V28M. 2, 66 Among these mutants, D18G and A25T are highly unstable and aggregation-prone. 60, 61 The observed chemical shift changes also suggest that the AB loop perturbations may propagate across the DAGH β-sheet to A109, L110 and V71, and thence to S117 in the strong dimer interface (Fig.…”

Transthyretin Asp38Tyr: a new mutation associated to a late onset neuropathy

“…Most Brazilian studies report only the TTR Val30Met variant, although at least three other variants causing FAP have been described in Brazil (TTR Val71Ala, TTR Ala19Asp, and TTR Ile107Val) (Marques et al ., ; Cruz , ; Ferreira et al ., ) . We report a novel TTR variant in two Brazilian sisters who developed a late onset neuropathy.…”

Amyloid Formation by Human Carboxypeptidase D Transthyretin-like Domain under Physiological Conditions

“…TTR tetrameric structure dissociates into dimers, which are unstable in the absence of additional quaternary interactions, explaining why TTR exists in primarily tetramer-monomer equilibrium (20,21). The monomers constitute the building blocks for amyloid fibril formation (22)(23)(24)(25).…”