Abstract
ABCB10 (ATP binding cassette sub-family B10) is a mitochondrial inner-membrane ABC transporter. ABCB10 has been shown to protect the heart from the impact of ROS during ischemia-reperfusion and to allow for proper hemoglobin synthesis during erythroid development. ABC transporters are proteins that increase ATP binding and hydrolysis activity in the presence of the transported substrate. However, molecular entities transported by ABCB10 and its regulatory mechanisms are currently unknown. Here we characterized ATP binding and hydrolysis properties of ABCB10 by using the 8-azido-ATP photolabeling technique. This technique can identify potential ABCB10 regulators, transported substrates and amino-acidic residues required for ATP binding and hydrolysis. We confirmed that Gly497 and Lys498 in the Walker A motif, Glu624 in the Walker B motif and Gly602 in the C-Loop motif of ABCB10 are required for proper ATP binding and hydrolysis activity, as their mutation changed ABCB10 8-Azido-ATP photo-labeling. In addition, we show that the potential ABCB10 transported entity and heme precursor delta-aminolevulinic acid (dALA) does not alter 8-azido-ATP photo-labeling. In contrast, oxidized glutathione (GSSG) stimulates ATP hydrolysis without affecting ATP binding, whereas reduced glutathione (GSH) inhibits ATP binding and hydrolysis. Indeed, we detectABCB10 glutathionylation in Cys547 and show that it is one of the exposed cysteine residues within ABCB10 structure. In all, we characterize essential residues for ABCB10 ATPase activity and we provide evidence that supports the exclusion of dALA as a potential substrate directly transported by ABCB10. Last, we show the first molecular mechanism by which mitochondrial oxidative status, through GSH/GSSG, can regulate ABCB10.
Highlights
The mitochondrial inner membrane protein ABCB10 or ABCme (ATP binding cassette B10 or mitochondrial erythroid) was initially identified when studying genes up-regulated during erythroid differentiation by the transcription factor GATA-1 [1]
8-azido-ATP [γ] biotin and [α-32P] 8-azido-ATP were synthetized by and purchased from Affinity Photoprobes (Lexington, KY); delta-aminolevulinic acid, reduced glutathione (GSH), oxidized glutathione (GSSG), ATP, ADP, AMP, CTP, GTP, TTP, anti-V5 agarose affinity gel beads and ExtrAvidin-peroxidase were from Sigma (Saint Louis, MO); Rabbit antiABCB10 mouse antibody was made by Research Genetics, Inc. (Huntsville, AL); Mouse anti-V5 antibody was from Invitrogen (Carlsbad, CA); Rabbit antiporin/VDAC mouse antibody was from Abcam (Cambridge, MA)
In some ABC transporters, ATP binding was found to be stabilized by hydrogen bond interactions of the oxygen atoms from the β- and γ-phosphates of ATP with the conserved glycine and lysine residues in the Walker A motif [11]
Summary
The mitochondrial inner membrane protein ABCB10 or ABCme (ATP binding cassette B10 or mitochondrial erythroid) was initially identified when studying genes up-regulated during erythroid differentiation by the transcription factor GATA-1 [1]. ABCB10 is expressed in non-erythroid tissues, such as the heart, which suggests a role of ABCB10 beyond hemoglobin synthesis. In this regard, inactivation of one allele of ABCB10 did not affect basal cardiac function, but markedly decreased heart recovery after acute induction of oxidative stress by ischemia-reperfusion. Inactivation of one allele of ABCB10 did not affect basal cardiac function, but markedly decreased heart recovery after acute induction of oxidative stress by ischemia-reperfusion These cardiac defects induced by ischemia-reperfusion in ABCB10 +/- hearts were completely prevented by a 20 minutes pre-treatment with antioxidants [4]. The exact mechanism by which ABCB10 protects mitochondria from oxidative stress has not been identified, as the molecular entities transported by ABCB10 remain elusive
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