CHEMISTRY/BIOCHEMISTRY. For the article “Chemistry for the analysis of protein–protein interactions: Rapid and efficient cross-linking triggered by long wavelength light” by David A. Fancy and Thomas Kodadek, which appeared in number 11, May 25, 1999, of Proc. Natl. Acad. Sci. USA (96, 6020–6024), the authors note the following: One of the intermediates in Fig. 1 was drawn incorrectly. The corrected figure and its legend are shown below. This change has no effect on the conclusions stated in the paper.
Figure 1.
Mechanism-based design of a photo-initiated protein cross-linking reaction. The top left part of the figure represents schematically the electron flow when Ru(II)bpy32+ (structure shown at the top right of the figure) is photolyzed in the presence of a persulfate, generating Ru(III) and sulfate radical. Ru(III) is a potent one-electron oxidant and would be expected to oxidize residues such as tyrosine. The resultant radical could proceed to form cross-linked products between two associated proteins by at least two mechanisms, as shown in the figure. If another tyrosine residue is nearby, then arene coupling would be expected. Alternatively, a nearby nucleophilic lysine or cysteine group could attack the radical to eventually provide a heteroatom-arene linkage. In each case, a hydrogen atom must be lost to form stable products, and the sulfate radical produced during Ru(III) formation could play a key role in this step. This figure represents only mechanistic hypotheses on which the reaction was designed. The true mechanism of Ru(II)bpy32+/persulfate-mediated cross-linking remains to be determined experimentally.