Dynamic cycling with a unique Hsp90/Hsp70-dependent chaperone machinery and GAPDH is needed for heme insertion and activation of neuronal NO synthase

Heme metabolism in nonerythroid cells

“…GAPDH therefore likely acts to both buffer and shuttle heme to apo-hemoproteins. Similar studies have shown the importance of GAPDH in heme insertion into soluble guanylate cyclase beta (sGCβ), inducible nitric oxide synthase (NOS), neuronal NOS, tryptophan 2-3-dioxygenase (TDO), indoleamine 2,3-dioxygenase (IDO), and globins ( 73 , 74 , 75 , 76 , 77 , 78 ). In most of these cases, heme insertion into the apoprotein is facilitated by chaperone proteins such as heat shock protein 90 and alpha hemoglobin stabilizing protein ( Fig.…”

Heme allocation in eukaryotic cells relies on mitochondrial heme export through FLVCR1b to cytosolic GAPDH

“…After GAPDH obtains heme it dissociates from the mitochondria, which enables it to transport heme and make it available to numerous client proteins that are located in the cytosol or in other cell compartments. The target heme proteins are present in cells in their heme-free states and are typically are in complex with the cell chaperone Hsp90, which drives their heme insertions in an ATP-dependent manner, possibly with assistance from co-chaperone proteins 13,35 . Hsp90 then dissociates from the heme-replete mature proteins, allowing their biological function 18 .…”

“…Because heme is chemically reactive and has promiscuous binding properties, its synthesis is tightly controlled and its intracellular transport has long been imagined to involve macromolecular carriers 2,4,5 . Of all the proteins or other macromolecules that have been proposed, the protein glyceraldehyde phosphate dehydrogenase (GAPDH), an enzyme in the glycolytic pathway that is ubiquitously expressed and known to perform alternative moonlighting functions [6][7][8] , has recently emerged as a premier intracellular heme chaperone 9 , based on findings that GAPDH binding of mitochondrially-generated heme is required for and coupled to intracellular heme delivery to numerous targets including hemoglobins α, β, and γ 10 , myoglobin 10 , nitric oxide synthases [11][12][13] soluble guanylyl cyclase β-subunit (sGCβ) 14 , cytochromes P450 15 , heme oxygenase 2 16 , indoleamine dioxygenase 1 (IDO1) and tryptophan dioxygenase (TDO) 17 . Insertion of the GAPDH-sourced heme into recipient target proteins is the final downstream step in heme delivery, and is now understood to require the cell chaperone protein Hsp90, which is typically bound to the heme-free (apo-) forms of the recipient proteins and drives their heme insertions in an ATP-driven process 18 .…”

Visualizing Mitochondrial Heme Flow through GAPDH to Targets in Living Cells and its Regulation by NO

“…Due to the physical and chemical properties of heme, its transport in cells has long been expected to involve a protein chaperone (1)(2)(3)(4)(5). Recently, the glycolytic enzyme GAPDH was shown to fulfill this role by binding mitochondrial heme and enabling its delivery to diverse targets including hemoglobin α, β, and γ, myoglobin, tryptophan dioxygenase (TDO), indoleamine dioxygenase 1 (IDO1), soluble guanylyl cyclase (sGC), NO synthases, and heme oxygenase 2 (6)(7)(8)(9)(10)(11)(12). In most cases, the heme insertions into these proteins also required the cell chaperone Hsp90 and its ATPase activity (13).…”