Labile Metal Pools
Some metals are trafficked by binding to “chaperone” proteins in the cytosol which deliver them to various recipient proteins. However, “labile metal pools” (LMPs) are also involved in trafficking although their exact roles are less well understood. LMPs consist of small metal complexes with nonproteinaceous ligands. They were discovered 50 years ago, but little is known regarding their chemical compositions or structures. We are using liquid- chromatography interfaced with inductively-coupled plasma mass spectrometry (LC-ICP-MS) to detect, identify, and characterize these pools. This is challenging because of the inherent lability of the complexes – they tend to fall apart as they migrate through chromatography columns. Many of these complexes are redox-active, such that the LC must be located in an anaerobic glove box. We have invented various methods for dealing with this problem, and are making progress on identifying these pools, by interfacing with electrospray ionization mass spectrometry (ESI-MS). We also use various genetic strains of yeast to probe the cellular functions of these pools.
In the future, we want to examine labile metal pools in human cytosol and other organelles using our LC-ICP-MS system. We suspect that these pools will be similar to those in yeast, but there are indications that imply significant differences. These studies would have direct relevance to various metal-associated diseases in which trafficking has become dysregulated. On a more practical side, we will continue to explore the effect of non-aqueous solvents on these pools; our goal is to find conditions causing these complexes to remain intact thereby allowing unambiguous chemical identification using downstream powerful analytical tools such as ESI-MS and NMR spectroscopy. Most of our studies have used size-exclusion chromatography (SEC) columns, but in the future, hydrophilic interaction chromatography (HILIC) and other types of chromatography will be explored. We are considering purchasing a dedicated ESI-MS that would allow us to characterize the metal-related metabolome of the cell. This would be a huge advantage in our quest to characterize these mysterious labile metal pools.