Glutathione binding to the Bcl-2 homology-3 domain groove - A molecular basis for Bcl-2 antioxidant function at mitochondria

Bcl-2 protects cells against mitochondrial oxidative stress and subsequent apoptosis. However, the mechanism underlying the antioxidant function of Bcl-2 is currently unknown. Recently, Bax and several Bcl-2 homology-3 domain (BH3)-only proteins (Bid, Puma, and Noxa) have been shown to induce a pro-oxidant state at mitochondria (1-4). Given the opposing effects of Bcl-2 and Bax/BH3-only proteins on the redox state of mitochondria, we hypothesized that the antioxidant function of Bcl-2 is antagonized by its interaction with the BH3 domains of pro-apoptotic family members. Here, we show that BH3 mimetics that bind to a hydrophobic surface (the BH3 groove) of Bcl-2 induce GSH-sensitive mitochondrial dysfunction and apoptosis in cerebellar granule neurons. BH3 mimetics displace a discrete mitochondrial GSH pool in neurons and suppress GSH transport into isolated rat brain mitochondria. Moreover, BH3 mimetics and the BH3-only protein, Bim, inhibit a novel interaction between Bcl-2 and GSH in vitro. These results suggest that Bcl-2 regulates an essential pool of mitochondrial GSH and that this regulation may depend upon Bcl-2 directly interacting with GSH via the BH3 groove. We conclude that this novel GSH binding property of Bcl-2 likely plays a central role in its antioxidant function at mitochondria.