TY - JOUR
T1 - Evidence for the cation-π interaction between Cu2+ and tryptophan
AU - Yorita, Hanami
AU - Otomo, Kohei
AU - Hiramatsu, Hirotsugu
AU - Toyama, Akira
AU - Miura, Takashi
AU - Takeuchi, Hideo
PY - 2008/11/19
Y1 - 2008/11/19
N2 - The cation-π interaction, a noncovalent interaction of electrostatic nature between a cation and an electron-rich π system, is increasingly recognized as an important force that influences the structures and functions of molecules including proteins. Unlike other metal cations, the transition metal cation Cu2+ is not regarded to take part in a cation-π interaction because Cu2+ tends to oxidize the π electron system, in particular that of Trp, and to introduce covalency in the metal-π electron interaction. This paper reports the first spectral evidence for the cation-π interaction between Cu2+ and Trp. The Cu2+ ion bound to the amino N-terminal Cu2+/Ni2+ binding motif composed of three amino acid residues interacts with the indole ring of the fourth Trp residue in a noncovalent manner. The Cu2+-Trp interaction produces a distinct negative band at 223 nm in circular dichroism (CD), which disappears upon mutation or depletion of the Trp residue or upon replacement of the Cu2+ ion by Ni2+. In UV absorption, a pair of negative/positive intensity changes is generated at 222/231 nm by the Cu2+-Trp interaction, being consistent with the previous observations on the indole ring interacting with K+ or a cationic His imidazole ring. The negative CD band around 223 nm is characteristic of the Cu2+-Trp pair and may be useful as a marker of the Cu2+-Trp cation-π interaction. Coordination of negatively charged ligands to Cu2+ is suggested to be important for the cation to be involved in a cation-π interaction.
AB - The cation-π interaction, a noncovalent interaction of electrostatic nature between a cation and an electron-rich π system, is increasingly recognized as an important force that influences the structures and functions of molecules including proteins. Unlike other metal cations, the transition metal cation Cu2+ is not regarded to take part in a cation-π interaction because Cu2+ tends to oxidize the π electron system, in particular that of Trp, and to introduce covalency in the metal-π electron interaction. This paper reports the first spectral evidence for the cation-π interaction between Cu2+ and Trp. The Cu2+ ion bound to the amino N-terminal Cu2+/Ni2+ binding motif composed of three amino acid residues interacts with the indole ring of the fourth Trp residue in a noncovalent manner. The Cu2+-Trp interaction produces a distinct negative band at 223 nm in circular dichroism (CD), which disappears upon mutation or depletion of the Trp residue or upon replacement of the Cu2+ ion by Ni2+. In UV absorption, a pair of negative/positive intensity changes is generated at 222/231 nm by the Cu2+-Trp interaction, being consistent with the previous observations on the indole ring interacting with K+ or a cationic His imidazole ring. The negative CD band around 223 nm is characteristic of the Cu2+-Trp pair and may be useful as a marker of the Cu2+-Trp cation-π interaction. Coordination of negatively charged ligands to Cu2+ is suggested to be important for the cation to be involved in a cation-π interaction.
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U2 - 10.1021/ja807010f
DO - 10.1021/ja807010f
M3 - Article
C2 - 18939840
AN - SCOPUS:56449093681
VL - 130
SP - 15266
EP - 15267
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 46
ER -