title: A luminescent cyclometalated iridium(III) complex accumulates in mitochondria and induces mitochondrial shortening by conjugation to specific protein targets.
abstract: We report the cellular properties of a luminescent cyclometalated iridium(III) complex, [Ir(pq)(2)(phen-ITC)](PF(6)) (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.
authors.affiliation: Department of Biology and Chemistry, City University of Hong Kong, Kowloon, PR China.
authors.forename: Baojiang
authors.initials: B
authors.lastname: Wang
authors.forename: Yimin
authors.initials: Y
authors.lastname: Liang
authors.forename: Hongjuan
authors.initials: H
authors.lastname: Dong
authors.forename: Tianfeng
authors.initials: T
authors.lastname: Tan
authors.forename: Bao
authors.initials: B
authors.lastname: Zhan
authors.forename: Jinping
authors.initials: J
authors.lastname: Cheng
authors.forename: Kenneth Kam-Wing
authors.initials: KK
authors.lastname: Lo
authors.forename: Yun Wah
authors.initials: YW
authors.lastname: Lam
authors.forename: Shuk Han
authors.initials: SH
authors.lastname: Cheng
mesh_terms: D016475:3T3 Cells; D000818:Animals; D002470:Cell Survival / Q000187:drug effects; D056831:Coordination Complexes / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology* / Q000633:toxicity; D007495:Iridium / Q000737:chemistry*; D049408:Luminescent Agents / Q000737:chemistry*; D051379:Mice; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism*; D009942:Organometallic Compounds / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology* / Q000633:toxicity; D011485:Protein Binding; D040901:Proteomics; D013379:Substrate Specificity; D050995:Voltage-Dependent Anion Channel 1 / Q000378:metabolism*
chemical_list: D056831:Coordination Complexes; D049408:Luminescent Agents; D009942:Organometallic Compounds; D007495:Iridium; D050995:Voltage-Dependent Anion Channel 1