Oxidative dimerization of proteins: role of tyrosine accessibility.
OBJECTIVE
To investigate the importance of two possible mechanisms of tyrosine oxidation on the yield of protein dimerization. The model chosen is hen and turkey egg-white lysozymes, which differ by seven amino acids, among which one tyrosine is in the 3 position.


METHODS
Aqueous solutions of proteins were oxidized by OH(*) or N(*)(3) free radicals produced by gamma or pulse irradiation in an atmosphere of N(2)O. Protein dimers were quantified by SDS-PAGE and reverse-phase HPLC. Dityrosines were identified by absorption and fluorescence.


RESULTS
Using N(*)(3) free radicals, the initial yields of dimerization are equal to (8.6 +/- 0.7) x 10(-9) mol J(-1) for both proteins. Using OH(*) free radicals, they become equal to (1.23 +/- 0.1) x 10(-8) and (4.42 +/- 0.1) x 10(-8) mol J(-1) for hen and turkey egg-white lysozymes, respectively (gamma radiolysis). DISCUSSION. N(*)(3) radicals react primarily with tryptophan residues only. Tyrosine gets oxidized by intramolecular long-range electron migration, whereas OH(*) may react directly with tyrosines. We propose a low participation of Tyr3 in turkey protein in the intramolecular process, because Tyr3 is far from all tryptophans. On the other hand, Tyr3 is very accessible to solvent and in a flexible area; thus collisions with OH(*) could easily be followed by intermolecular dimerization.
Audette
M
M
LPCR, UMR 8610 CNRS-Université, Bât. 350, Centre Universitaire, Orsay Cedex, F-91405, France.
Blouquit
Y
Y
Houée-Levin
C
C
D000818:Animals; D002645:Chickens; D019281:Dimerization; D005260:Female; D005609:Free Radicals / Q000737:chemistry; D017665:Hydroxyl Radical / Q000737:chemistry; D066298:In Vitro Techniques; D008958:Models, Molecular; D009113:Muramidase / Q000737:chemistry; D009584:Nitrogen / Q000737:chemistry; D010084:Oxidation-Reduction; D020836:Protein Structure, Quaternary; D011506:Proteins / Q000737:chemistry*; D014422:Turkeys; D014443:Tyrosine / Q000737:chemistry*
D005609:Free Radicals; D011506:Proteins; D017665:Hydroxyl Radical; D014443:Tyrosine; D009113:Muramidase; D009584:Nitrogen