Intermediate filament proteins are targets for crosslinking in the lens by the endogenous transglutaminase

Purpose. N^ε(γ-glutamyl)lysine crosslinks, the characteristic hallmarks for the transglutaminase-mediated polymerization of proteins, were isolated from high molecular weight products in human cataract (Proc. Natl. Acad. Sci. USA 78, 1356, 1981). Subsequently, our attention focused on the participation of highly select subsets of subunits from the β_H, β_L and αB crystallin classes as donor and/or acceptor substrates for crosslinking by the endogenous enzyme of the lens (rabbit and calf; see Biochemistry 24, 1525, 1985; ibid 26, 4629, 1987; Invest. Ophthalmol. Vis. Sci. 28, 1218, 1987; Biochim. Biophys. Acta 1040, 187, 1990; Proc. Natl. Acad. Sci. USA 87, 8472, 1990; ibid 88, 82, 1991; ibid 89, 11161, 1992; Bioconjugate Chem. 3, 37, 1992). This approach is now being extended to examine the reactivities of the intermediate filament constituents of the lens with transglutaminase. Results. Crosslinking, donor and acceptor labelling experiments will be presented for the reactions of (1) the purified protein substrates: recombinant human vimentin expressed in E. coli, bovine lens vimentin and bovine lens filensin, with a tissue type of transglutaminase obtained from guinea pig liver and, more significantly, (2) with the endogenous calf lens transglutaminase acting on the intermediate filament constituents in the tissue upon activation by Ca²⁺-ions. Conclusions. Intermediate filament proteins are substrates for transglutaminase.