Carbamylation promotes amyloidogenesis and induces structural changes in Tau-core hexapeptide fibrils

• Published in: Biochimica et biophysica acta. General subjects Vol. 1862; no. 12; pp. 2590 - 2604
• Main Authors: Guru KrishnaKumar, V., Baweja, Lokesh, Ralhan, Krittika, Gupta, Sharad
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01-12-2018
• Subjects: Aggregation; Amyloids; Carbamylation; Peptide; Structural changes; Aggregation; Carbamylation; Structural changes; Amyloids; Peptide
• ISSN: 0304-4165; 1872-8006
• DOI: 10.1016/j.bbagen.2018.07.030

Carbamylation is a non-enzymatic post-translational modification (PTM), which involves the covalent modification of N-terminus of protein or ε-amino group of Lys. The role of carbamylation in several age-related disorders is well documented, however, the relationship between carbamylation and neurodegenerative disorders including Alzheimer's disease remains uncharted.
In the present study, using aggregation-prone tau-core hexapeptide fragments 306VQIVYK311 (PHF6) and 275VQIINK280 (PHF6*) as models, we have elucidated the effect of carbamylation on aggregation kinetics and the changes occurring in the 3-dimensional architecture of fibrils using biophysical assays and molecular dynamics simulations.
We found that carbamylation aids in amyloid formation and can convert the unstructured off-pathway aggregates into robust amyloids, which were toxic to cells. Electron microscopy images and molecular dynamics simulations of PHF6 fibrils showed that carbamylated peptides can form excess hydrogen bonds and modulate the pitch length and twist of peptides fibrils. We have also compared N-terminal carbamylation to acetylation and further extended our finding to full length tau that exhibits aggregation upon carbamylation even in the absence of any external inducer.
Our in vitro and in silico results together suggest that carbamylation can modulate the aggregation pathway of the amyloidegenic sequences and cause structural changes in fibril assemblies.
Carbamylation acts as a switch, which triggers the aggregation in short amyloidogenic peptide fragments and modulate the structural changes in resulting amyloid fibrils.
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•Carbamylation is a non-enzymatic PTM involving the covalent modification of Nα-NH2 of protein or Nε-NH2 of Lys•The effect of carbamylation on aggregation of short amyloidogenic peptides and tau protein in vitro and in silico•Carbamylation acts as a switch which triggers the amyloidogenesis and converts off-pathway aggregates into amyloids•Electron Microscopy & Molecular Dynamics studies revealed that carbamylation modulated structural changes in PHF6 fibrils