Synthetic fluorescent probes for studying copper in biological systems

Abstract

The potent redox activity of copper is required for sustaining life. Mismanagement of its cellular pools, however, can result in oxidative stress and damage connected to aging, neurodegenerative diseases, and metabolic disorders. Therefore, copper homeostasis is tightly regulated by cells and tissues. Whereas copper and other transition metal ions are commonly thought of as static cofactors buried within protein active sites, emerging data points to the presence of additional loosely bound, labile pools that can participate in dynamic signalling pathways. Against this backdrop, we review advances in sensing labile copper pools and understanding their functions using synthetic fluorescent indicators. Following brief introductions to cellular copper homeostasis and considerations in sensor design, we survey available fluorescent copper probes and evaluate their properties in the context of their utility as effective biological screening tools. We emphasize the need for combined chemical and biological evaluation of these reagents, as well as the value of complementing probe data with other techniques for characterizing the different pools of metal ions in biological systems. This holistic approach will maximize the exciting opportunities for these and related chemical technologies in the study and discovery of novel biology of metals.

In vivo bioluminescence imaging of labile iron accumulation in a murine model of Acinetobacter baumannii infection

“…A modest response is observed with free copper salts, as is similarly observed for the related fluorescence probe FIP-1 (15). However, as a typical eukaryotic cell exhibits a ∼10-fold higher level of iron over copper coupled with the high buffering capacity of copper with glutathione and metallochaperones (picomolar to femtomolar K d values) (55)(56)(57)(58)(59)(60), the modest response to free copper salts suggests that ICL-1 should have sufficient selectivity to detect alterations in biological ferrous iron levels. ICL-1 is also selective for labile Fe 2+ over other biologically relevant forms of iron that are tightly bound to proteins and cofactors, such as transferrin, ferritin, hemin, and hemoglobin, as well as Fe 3+ , along with reductants glutathione, N-acetyl cysteine, β-mercaptoethanol, and ascorbic acid (Fig.…”

The Intestinal Copper Exporter CUA-1 Is Required for Systemic Copper Homeostasis in Caenorhabditis elegans

“…Staining with the Copper Probe CF4 and LysoTracker-The Copper Fluor-4 (CF4) sensor combines a piperidine-substituted rhodol with a trifluoromethyl-substituted bottom ring bearing a thioether receptor, along with a matched control Copper Fluor-4 (Control CF4) dye that lacks the copper-responsive receptor to help distinguish between copper-dependent and dye-dependent responses (30,63). Replacement of the thioether-rich receptor arms for copper recognition in CF4 by isostructural octyl groups in control CF4 provides a mimic of the size, shape, and hydrophobicity of thioethers but do not bind copper, offering a matched pair of probes to disentangle copper-dependent fluorescence responses from potential dyedependent ones.…”

In vivo bioluminescence imaging reveals copper deficiency in a murine model of nonalcoholic fatty liver disease

“…This same redox activity also poses a potential danger, requiring highly orchestrated regulation of copper pools to prevent oxidative stress and free radical damage events that are detrimental to health (12)(13)(14)(15)(16)(17)(18). Indeed, genetic disorders that disrupt copper homeostasis lead to severe and lethal conditions such as Menkes and Wilson's diseases (13,19,20), and imbalances in physiological copper levels and tissue miscompartmentalization arising from genetic and/or dietary factors are correlated with cancer, neurodegenerative diseases, and metabolic disorders such as obesity, diabetes, and nonalcoholic fatty liver disease (NAFLD) (21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32).…”