A framework for the investigation of heme homeostasis through genetically encoded heme sensors

To meet the logistical needs of supply and demand for heme, organisms need to make it, move it to the right place, and degrade it when necessary. More specifically, the provision and distribution of heme must be coupled with the synthesis of heme proteins and meticulously regulated so that heme-tuned cellular pathways are only activated on demand. However, how cells handle heme to meet transient cellular requirements is yet to be clarified and represents a long-lasting question in bioinorganic chemistry. This study deploys a genetically encoded heme sensor (mAPXmEGFP) and Fluorescence Lifetime Imaging Microscopy to investigate the cellular mechanisms controlling heme bioavailability. The analysis is paired with the contextualisation of the data within the intricate network of regulation that oversees the levels of key proteins (i.e. ALAS1, HO-1, HO-2, and GAPDH) and their coordination with an intracellular heme buffering system that ensures heme homeostasis. Further, the implications and possible drawbacks deriving from the deployment of genetically encoded sensors in live cells is discussed and explored.