Comparison of two phenotypically distinct lattice corneal dystrophies caused by mutations in the transforming growth factor beta induced (TGFBI) gene.

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In this study , we investigated whether the phenotypic difference observed between two lattice corneal dystrophy type 1 (LCD type 1 ) cases caused by either a single A 546 D substitution or an A 546 D /P 551 Q double substitution in TGFBIp (transforming growth factor beta induced protein ) can be ascribed to (i ) a difference in the proteomes of corneal amyloid deposits , (ii ) altered proteolysis of TGFBIp , or (iii ) structural changes of TGFBIp introduced by the P 551 Q amino acid substitution .A myloid deposits were isolated from the corneas of two siblings with LCD type 1 resulting from A 546 D /P 551 Q mutations in the TGFBI gene using laser capture microdissection and subsequently analyzed by LC -MS /MS . Proteolytic processing of TGFBIp was addressed by counting peptide spectra . Lastly , to study the possible effect of the P 551 Q substitution , recombinant FAS 1 -4 domain variants were subjected to in vitro stability assays .The amyloid proteomes and TGFBIp processing of the two A 546 D /P 551 Q LCD type 1 cases were similar to each other as well as to the A 546 D amyloid proteome previously reported by us . The stability assays revealed a minor destabilization of the FAS 1 -4 domain upon the addition of the P 551 Q mutation , moreover , it resulted in different accessibility to tryptic cleavage sites between the A 546 D and A 546 D /P 551 Q mutant FAS 1 -4 domain variants .T he difference in A 546 D and A 546 D /P 551 Q LCD type Â 1 phenotypes can not be ascribed to altered corneal amyloid composition or altered in vivo proteolytic processing of TGFBIp . Instead , a small difference in thermodynamic stability introduced by the P 551 Q mutation most likely causes structural changes of TGFBIp . The MS proteomics data have been deposited to the ProteomeXchange with identifier PXD 000307 (http ://proteomecentral .proteomexchange .org /dataset /PXD 000307 ).