A luminescent cyclometalated iridium(III) complex accumulates in mitochondria and induces mitochondrial shortening by conjugation to specific protein targets

Baojiang WANG, Yimin LIANG, Hongjuan DONG, Tianfeng TAN, Bao ZHAN, Jinping CHENG, Kenneth Kam Wing LO, Yun Wah LAM, Shuk Han CHENG

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38 Citations (Scopus)

Abstract

We report the cellular properties of a luminescent cyclometalated iridium(III) complex, [Ir(pq)₂(phen-ITC)](PF₆) (Ir-ITC; Hpq=2-phenylquinoline, phen-ITC=5-isothiocyanate-1,10-phenanthroline), that efficiently and specifically labels mitochondria in living mammalian cells. Ir-ITC can be covalently conjugated to its protein targets, and its luminescence survived cell lysis, protein extraction, and gel electrophoresis under denaturing conditions. The conjugation of Ir-ITC with live-cell proteins is rapid and highly selective; the process requires active cellular metabolism, as the conjugation is abolished at nonphysiological temperature or in the presence of sodium azide. Based on measurements of the luminescence intensity, we have devised a biochemical fractionation procedure that allows the enrichment of the conjugated proteins, and their subsequent separation by two-dimensional gel electrophoresis (2DGE). Luminescent protein spots were picked from the gel and analyzed by mass spectrometry; this resulted in the identification of 46 proteins. Many of the strongly luminescently labeled proteins are mitochondrial proteins. One of the targets is VDAC1 (voltage-dependent anion channel 1). Consistent with known phenotypes of VDAC1 deregulation, prolonged exposure of cells to Ir-ITC led to significant mitochondrial shortening and fragmentation. As far as we know, this is the first report on the molecular characterization of the interactions of a luminescent dye with its biological targets. As many biological dyes exhibit specific intracellular staining patterns, the identification of their molecular targets can help elucidate the mechanisms behind their staining specificities and cytotoxicity. We believe our biochemical approach can be applied to identify the targets of a wide range of fluorescent and luminescent probes. Copyright © 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Original languageEnglish
Pages (from-to)2729-2737
JournalChemBioChem
Volume13
Issue number18
Early online date15 Dec 2012
DOIs
Publication statusPublished - Dec 2012

Citation

Wang, B., Liang, Y., Dong, H., Tan, T., Zhan, B., Cheng, J., . . . Cheng, S. H. (2012). A luminescent cyclometalated iridium(III) complex accumulates in mitochondria and induces mitochondrial shortening by conjugation to specific protein targets. ChemBioChem, 13(18), 2729-2737. doi: 10.1002/cbic.201200517

Keywords

  • 2DGE
  • Fluorescent probes
  • Iridium
  • Luminescence
  • Mitochondrial fission

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