BIGH3 (TGFBI) Arg124 mutations influence the amyloid conversion of related peptides in vitro

Amyloid deposits with Arg124 mutated TGFBI protein have been identified in autosomal dominant blinding corneal dystrophies. We assessed in vitro the mechanisms determining TGFBI protein amyloid transformation involving mutations of Arg124. Eight peptides synthesized following the TGFBI protein sequence, centered on codon Arg124 holding the previously reported amyloidogenic mutations and the respective controls were studied. Cys124 and His124 mutated peptide preparations contained significantly higher amounts of amyloid than the native peptide. Blocking the SH group of Cys124 and deleting the first four NH2-terminal amino acids including Val112-Val113 resulted in a decrease in amyloid fibril formation while deletion of the nine CONH2-terminal residues increased amyloid fibril concentration. Fourrier transformed-infrared spectroscopy analysis of the different peptide solutions showed an increase in beta-pleated sheet structures in those with enhanced amyloid yielding. We designed a peptide (BB1) likely to counteract the role of Val112-Val113 in amyloid fibril formation. Incubation of Cys124 peptide with BB1 indeed resulted in a 35% inhibition of amyloid fibril formation. Our results are in keeping with the clinical observations of Arg124 mutation-linked amyloidosis and show the importance of Val112-Val113, disulfide and hydrogen bonding in increasing the beta-pleated conformation and amyloid formation. These findings shed new light on the molecular mechanisms of TGFBI protein amyloidogenesis and encourage further research on the use of specifically designed peptides as putative therapeutic agents for these disabling diseases.