Analysis of the data on titration of native and peroxynitrite modified αA- and αB-crystallins by Cu(2+)-ions

The interaction of αA- and αB-crystallins with Cu(2+) ion modulates their structure and chaperone-like activity which is important for lens transparency. Theoretical analysis of the dependences of fluorescence intensity of native αA- and αB-crystallins and αA- and αB-crystallins modified by peroxynitrite on concentration of Cu(2+) ions has been carried out. It has been shown that one subunit of native αA-crystallin contains two equivalent Cu(2+)-binding sites. The microscopic dissociation constant for Cu(2+)–αA-crystallin complex (K(diss)) was found to be equal to 9.7 µM. For peroxynitrite modified αA-crystallin the K(diss) value is equal to 17 µM. One subunit of native αB-crystallin contains two non-equivalent Cu(2+)-binding sites. The corresponding microscopic dissociation constants for Cu(2+)–αB-crystallin complexes (K(1) and K(2)) were found to be equal to 0.94 and 36 µM. For peroxynitrite modified αB-crystallin the K(1) and K(2) values are equal to 4.3 and 70 µM, respectively.