Participation of tryptophan 62 in the self-association of hen egg white lysozyme. Application of natural abundance carbon 13 nuclear magnetic resonance spectroscopy

Abstract

Self-association of hen egg white lysozyme in solution of 38 degrees) is examined by means of natural abundance 13C nuclear magnetic resonance spectroscopy. The effect of pH on the resonances of the nonprotonated aromatic carbons of 9 mM lysozyme, and the effect of protein concentration (at pH 7) on these resonances, both indicate that self-association significantly affects the chemical shift of Cgamma of Trp-62, but not the chemical shifts of the other nonprotonated aromatic carbons. This result is consistent with the reported participation of Trp-62 in the intermolecular contact (Banerjee, S.K., Pogolotti, A., and Rupley, J.A. (1975) J. Biol. Chem. 250, 8260-8266). Our results indicate that the resonance of Cgamma or Trp-62 is a convenient monitor of lysozyme self-association. The chemical shift of this resonance reflects the extent of aggregation, while the line width yields information about the lifetime of the intermolecular contact. This lifetime is 1 to 2 ms at 38 degrees (9 mM protein, 0.1 M NaCl, pH 7). Our results also indicate that self-association of lysozyme is not accompanied by any general conformational change, and that binding of a lanthanide ion (at the metal ion binding site near the carboxylate groups of ASP-52 AND Glu-35) strongly suppresses self-association.