Lens transglutaminase selects specific beta-crystallin sequences as substrate.

Abstract
[3H]Methylamine was used as a convenient probe for transglutaminase (EC 2.3.2.13) activity to explore the action of this enzyme in the bovine eye lens. The glutamine residues acting as acyl-donor sites in 3 .beta.-crystalline chains, which are the only substrates for lens transglutaminase among the various lens-specific structural proteins, the crystallins. A single glutamine was found to bind [3H]methylamine in each of these 3 chains: glutamine .sbd.9 in .beta.Bp (.beta.B2), glutamine .sbd.21 in .beta.B3, and glutamine .sbd.23 or .sbd.24 in .beta.A3. The 4 glutamines are all located in the NH2-terminal regions, which presumably extend from the compact 2-domain structure of the .beta.-crystallin chains. It was established that several components of the lens cytoskeleton are substrates for transglutaminase.