Glyceraldehyde-3-phosphate dehydrogenase is a chaperone that allocates labile heme in cells

Abstract

Cellular heme is thought to be distributed between a pool of sequestered heme that is tightly bound within hemeproteins and a labile heme pool required for signaling and transfer into proteins. A heme chaperone that can hold and allocate labile heme within cells has long been proposed but never been identified. Here, we show that the glycolytic protein glyceraldehyde-3-phosphate dehydrogenase (GAPDH) fulfills this role by acting as an essential repository and allocator of bioavailable heme to downstream protein targets. We identified a conserved histidine in GAPDH that is needed for its robust heme binding both and in mammalian cells. Substitution of this histidine, and the consequent decreases in GAPDH heme binding, antagonized heme delivery to both cytosolic and nuclear hemeprotein targets, including inducible nitric-oxide synthase (iNOS) in murine macrophages and the nuclear transcription factor Hap1 in yeast, even though this GAPDH variant caused cellular levels of labile heme to rise dramatically. We conclude that by virtue of its heme-binding property, GAPDH binds and chaperones labile heme to create a heme pool that is bioavailable to downstream proteins. Our finding solves a fundamental question in cell biology and provides a new foundation for exploring heme homeostasis in health and disease.

Biochemical and Structural Characterization of XoxG and XoxJ and Their Roles in Lanthanide‐Dependent Methanol Dehydrogenase Activity

“…PQQ is synthesized in the cytosol, but the proteins that use it are periplasmic . It is unknown how PQQ gets to the periplasm, but the reactivity of PQQ with nucleophiles at its C5 position would likely necessitate a chaperoned process, as is the case for other reactive enzyme cofactors such as heme and iron–sulfur clusters …”

From Synthesis to Utilization: The Ins and Outs of Mitochondrial Heme

“…However, the molecules and mechanisms that mobilize heme from its site of synthesis are not well defined. Recent work supports the role of a number of proteins in this distribution, including glyceraldehyde phosphate dehydrogenase (GAPDH) [91,92], PGRMC1 [83] and PGRMC2 [90]. Further, it is unclear how the demand for heme in different cellular locations regulates the distribution of heme from FECH.…”

The heme biosynthetic enzyme, 5-aminolevulinic acid synthase (ALAS), and GTPases in control of mitochondrial dynamics and ER contact sites, regulate heme mobilization to the nucleus

“…The heme trafficking kinetics data challenge the current conceptual paradigm for the cellular distribution of mitochondrial heme. The discovery of the first putative mitochondrial heme exporter, Flvcr1b, the only mitochondrial heme transporter identified to date (Chiabrando et al, 2012), has often been taken to imply that heme distribution is sequential, with heme first transported into the cytosol followed by its mobilization to other organelles (Hanna et al, 2017; Reddi and Hamza, 2016; Sweeny et al, 2018). However, we found that heme distribution to the mitochondrial matrix, cytosol, and nucleus occurs virtually simultaneously, suggesting the existence of parallel pathways for heme mobilization to different cellular locales ( Fig.…”

“…Herein, using genetically encoded ratiometric fluorescent h eme s ensors (HS1) targeted to the mitochondrial matrix, cytosol, or nucleus (Hanna et al, 2016; Hanna et al, 2018; Sweeny et al, 2018), we developed a live-cell assay in yeast to monitor heme distribution kinetics to probe the role of ALAS and ER-mitochondrial contact sites and dynamics on subcellular heme trafficking. Surprisingly, we find that heme trafficking rates from the matrix side of the IM to the mitochondrial matrix and cytosol are similar, while trafficking to the nucleus is ∼25% faster.…”