Abstract
π–π stacking interaction is well-known to be one of the weak interactions. Its importance in the stabilization of protein structures and functionalization has been reported for various systems. We have focused on a single copper oxidase, galactose oxidase, which has the π–π stacking interaction of the alkylthio-substituted phenoxyl radical with the indole ring of the proximal tryptophan residue and catalyzes primary alcohol oxidation to give the corresponding aldehyde. This stacking interaction has been considered to stabilize the alkylthio-phenoxyl radical, but further details of the interaction are still unclear. In this review, we discuss the effect of the π–π stacking interaction of the alkylthio-substituted phenoxyl radical with an indole ring.
Highlights
IntroductionThe active form of galactose oxidase (GO) is known to be the copper(II)-alkylthiophenoxyl radical, and this phenoxyl radical has been proposed to be stabilized by π–π stacking interaction with the indole ring of the proximal tryptophan residue (Trp 290) [37]
The roles of the π–π stacking interaction in the metal-phenoxyl radical complexes have been discussed in this review, especially focusing on the interaction of the alkylthiophenoxyl radical with the indole ring as seen in the single copper enzyme galactose oxidase (GO)
GO has an alkyltiophenoxyl radical bound to copper ions in the active site, and the indole moiety of Trp 290 located at the proximal position of the phenoxyl radical is involved in the π–π stacking interaction
Summary
The active form of GO is known to be the copper(II)-alkylthiophenoxyl radical, and this phenoxyl radical has been proposed to be stabilized by π–π stacking interaction with the indole ring of the proximal tryptophan residue (Trp 290) [37]. The indole ring of Trp 290 is located in the second coordination sphere most probably for stabilization of the copper(II)-alkylthiophenoxyl radical species by the of the active site of GO, most probably for stabilization of the copper(II)-alkylthiophenoxyl π–π stacking interaction with the alkylthiophenoxyl radical of Tyr 272 [57,58,59,60,61]. Cu(II) ion inwhere the activephenoxyl site, shows a significantly structure, especially in the active site, where the phenoxyl radical could not be detected and no C-S bond formation in the phenol of Tyr 272 was could foundnot
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