Fibril Core of Transforming Growth Factor Beta-Induced Protein (TGFBIp) Facilitates Aggregation of Corneal TGFBIp

Abstract

Mutations in the transforming growth factor beta-induced (TGFBI) gene result in a group of hereditary diseases of the cornea that are collectively known as TGFBI corneal dystrophies. These mutations translate into amino acid substitutions mainly within the fourth fasciclin 1 domain (FAS1-4) of the transforming growth factor beta-induced protein (TGFBIp) and cause either amyloid or non-amyloid protein aggregates in the anterior and central parts of the cornea, depending on the mutation. The A546T substitution in TGFBIp causes lattice corneal dystrophy (LCD), which manifests as amyloid-type aggregates in the corneal stroma. We previously showed that the A546T substitution renders TGFBIp and the FAS1-4 domain thermodynamically less stable compared with the wild-type (WT) protein, and the mutant FAS1-4 is prone to amyloid formation in vitro. In the present study, we identified the core of A546T FAS1-4 amyloid fibrils. Significantly, we identified the Y571-R588 region of TGFBIp, which we previously found to be enriched in amyloid deposits in LCD patients. We further found that the Y571-R588 peptide seeded fibrillation of A546T FAS1-4 and, more importantly, we demonstrated that native TGFBIp aggregates in the presence of fibrils formed by the core peptide. Collectively, these data suggest an involvement of the Y571-R588 peptide in LCD pathophysiology.

Effect of position-specific single-point mutations and biophysical characterization of amyloidogenic peptide fragments identified from lattice corneal dystrophy patients

“…Previous reports from Enghild and colleagues identified the presence of smaller peptide fragments of the protein accumulating in the cornea possibly due to aberrant proteolytic processing [ 15 , 16 , 18 ]. In particular, an increased abundance of peptide fragment L 128 –R 172 in patients' cornea carrying the R124C mutation was reported.…”

“…It has been hypothesized that the proteolytic products with high aggregation propensity may act as fibrillation seeds and trigger an aggregation cascade [ 17 ]. The increased abundance of a short peptide fragment in the 4th FAS-1 domain of TGFBIp (Y 571 HIGDEILVSGGIGALVR 588 ) in amyloid deposits and its ability to accelerate the fibrillation of the mutant protein confirmed the role of aberrant proteolytic fragments in accelerating the fibrillation of larger proteins [ 18 ]. The increased abundance of peptide fragments spanning the 4th FAS-1 domain of TGFBIp in the amyloid deposits of dystrophic patients further suggests the importance of this domain in pathophysiology [ 18 ].…”

“…Sørensen et al [ 18 ] characterized the amyloid fibril forming properties of TGFBIp F 515 –N 532 (F 515 SMLVAAIQSAGLTETLN 532 ) and Y 571 –R 588 (Y 571 HIGDEILVSGGIGALVR 588 ) that were enriched in the amyloid deposits in LCD patients with R124C, V624M and A546D mutations. They further showed that the peptide fragment Y 571 –R 588 accelerated the amyloid fibrillation of A546T mutant protein.…”

Transforming growth factor beta‐induced p.(L558P) variant is associated with autosomal dominant lattice corneal dystrophy type IV in a large cohort of Spanish patients

“…Moreover, it has been reported that LCD variants, which have a delayed onset compared with classic LCD, are caused by distinct heterozygous amyloidogenic alterations, which are mainly located in the fourth FAS1 domain of TGFBI . In this line, the atypical pattern of corneal opacities associated with the p.(L558P) variant might be due in part to the potential amyloidogenic properties of the TGFBI peptide where the altered amino acid lies (Y571‐R588) …”

Genotype-Phenotype Correlation forTGFBICorneal Dystrophies Identifies p.(G623D) as a Novel Cause of Epithelial Basement Membrane Dystrophy

“…Once released, these peptides form amyloid fibrils, which subsequently aggregate. 30 Given the clinical and histologic variability associated with the p.(G623D) mutation, it would be interesting to further investigate the mutant protein to determine its thermodynamic stability and aggregation propensity.…”