Mutation in transforming growth factor beta induced protein associated with granular corneal dystrophy type 1 reduces the proteolytic susceptibility through local structural stabilization.

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Hereditary mutations in the transforming growth factor beta induced (TGFBI ) gene cause phenotypically distinct corneal dystrophies characterized by protein deposition in cornea . We show here that the Arg 555 T rp mutant of the fourth fasciclin 1 (FAS 1 -4 ) domain of the protein (TGFBIp /keratoepithelin /βig-h 3 ), associated with granular corneal dystrophy type 1 , is significantly less susceptible to proteolysis by thermolysin and trypsin than the WT domain . High -resolution liquid-state NMR of the WT and Arg 555 Trp mutant FAS 1 -4 domains revealed very similar structures except for the region around position 555 . The Arg 555 Trp substitution causes Trp 555 to be buried in an otherwise empty hydrophobic cavity of the FAS 1 -4 domain . The first thermolysin cleavage in the core of the FAS 1 -4 domain occurs on the N-terminal side of Leu 558 adjacent to the Arg 555 mutation . MD simulations indicated that the C-terminal end of helix α 3 ' containing this cleavage site is less flexible in the mutant domain , explaining the observed proteolytic resistance . This structural change also alters the electrostatic properties , which may explain increased propensity of the mutant to aggregate in vitro with 2 ,2 ,2 -trifluoroethanol . Based on our results we propose that the Arg 555 Trp mutation disrupts the normal degradation /turnover of corneal TGFBIp , leading to accumulation and increased propensity to aggregate through electrostatic interactions .