Recent evidence supports the theory that mitochondrial homeostasis is the key regulatory step in apoptosis through the actions of members of the Bcl-2 family. Pro-apoptotic members of the family, such as Bax, Bad and Bid, can induce the loss of outer-membrane integrity with subsequent redistribution of pro-apoptotic proteins such as cytochrome c that are normally located in the intermembrane spaces of mitochondria. The anti-apoptotic members of the family, such as Bcl-2 and Bcl-XL, protect the integrity of the mitochondrion and prevent the release of death-inducing factors. Bid normally exists in an inactive state in the cytosol, but after cleavage by caspase 8, the carboxy-terminal portion (tBid) moves from cytosol to mitochondria, where it induces release of cytochrome c. Here we address the question of what mediates specific targeting of tBid to the mitochondria. We provide evidence that cardiolipin, which is present in mitochondrial membranes, mediates the targeting of tBid to mitochondria through a previously unknown three-helix domain in tBid. These findings implicate cardiolipin in the pathway for cytochrome c release.

ATP binding cassette (ABC) transporters play critical roles in maintaining sterol balance in higher eukaryotes. The ABCG5/ABCG8 heterodimer (G5G8) mediates excretion of neutral sterols in liver and intestines1–5. Mutations disrupting G5G8 cause sitosterolaemia, a disorder characterized by sterol accumulation and premature atherosclerosis. Here we use crystallization in lipid bilayers to determine the X-ray structure of human G5G8 in a nucleotide-free state at 3.9 Å resolution, generating the first atomic model of an ABC sterol transporter. The structure reveals a new transmembrane fold that is present in a large and functionally diverse superfamily of ABC transporters. The transmembrane domains are coupled to the nucleotide-binding sites by networks of interactions that differ between the active and inactive ATPases, reflecting the catalytic asymmetry of the transporter. The G5G8 structure provides a mechanistic framework for understanding sterol transport and the disruptive effects of mutations causing sitosterolaemia.

Externalization of phosphatidylserine, which is normally restricted to the inner leaflet of plasma membrane, is a hallmark of mammalian apoptosis. It is not known what activates and mediates the phosphatidylserine externalization process in apoptotic cells. Here, we report the development of an annexin V-based phosphatidylserine labelling method and show that a majority of apoptotic germ cells in Caenorhabditis elegans have surface-exposed phosphatidylserine, indicating that phosphatidylserine externalization is a conserved apoptotic event in worms. Importantly, inactivation of the gene encoding either the C. elegans apoptosis-inducing factor (AIF) homologue (WAH-1), a mitochondrial apoptogenic factor, or the C. elegans phospholipid scramblase 1 (SCRM-1), a plasma membrane protein, reduces phosphatidylserine exposure on the surface of apoptotic germ cells and compromises cell-corpse engulfment. WAH-1 associates with SCRM-1 and activates its phospholipid scrambling activity in vitro. Thus WAH-1, after its release from mitochondria during apoptosis, promotes plasma membrane phosphatidylserine externalization through its downstream effector, SCRM-1.

CLE is a useful and potentially important method for the diagnosis and classification of GIM in vivo.

The newly identified specific V-ATPase inhibitor, salicylihalamide A, is distinct from any previously identified V-ATPase inhibitors in that it inhibits only mammalian V-ATPases, but not those from yeast or other fungi (Boyd, M. R., Farina, C., Belfiore, P., Gagliardi, S., Kim Acidification of intracellular compartments of eukaryotes is essential for many cellular processes, including receptor-mediated endocytosis, protein degradation in lysosomes, processing of hormones, uptake, and storage of neurotransmitters, and entry of many viruses into cells. The control of pH within these intracellular compartments is mediated by vacuolar H ϩ -translocating ATPases, which acidify organelles of both constitutive and regulated secretory pathways (1-5). V-ATPases 1 are also found in the plasma membrane of certain cells where they are responsible for cell type-specific processes, including urinary acidification and osteoclast-mediated bone resorption (6, 7). The V-type ATPases are among the most widely distributed ATP-driven ion pumps in nature, present in all eukaryotic cells and in various bacteria. Within eukaryotic cells, the structure of these proton pumps is highly conserved from yeast to human, as a multiple subunit complex with a molecular mass exceeding 850 kDa. They contain at least 13 different subunits with various copy numbers, which are organized into two distinct domains, a peripheral V 1 domain that is the catalytic sector and a transmembrane V 0 domain that constitutes the proton channel.V-pumps are regulated at various levels from transcription and protein synthesis to the regulation of its enzymatic activity through a variety of mechanisms. The most unique regulation mechanism for V-pumps is the reversible dissociation and association of V 1 and V 0 in response to energy demand, which has been extensively studied and clearly demonstrated in yeast and tobacco hornworm (8 -10). However, whether this reversible dissociation and association of V-ATPase domains exists in mammals as a regulatory mechanism and, if it does, how this process is regulated, is not clear at the present.During the past two decades, the importance of this class of ATPases for many critical cellular functions has become increasingly appreciated. Furthermore, the elucidation of the physiological role of V-pumps has revealed the important role these proteins play in a wide array of pathological processes, such as osteoporosis (6), certain renal diseases (7, 11), HIV infection (12), and tumor metastasis (5). The food vacuole of certain parasites is acidified by V-type proton pumps, and disruption of the acidification of this intracellular compartment results in death of the organism. Thus, the V-type pumps are potential targets for the development of pharmacological agents to treat a variety of diseases.Because of the importance of V-ATPases as a potential therapeutic target, the mechanism by which inhibitors of V-ATPase interfere with pump function has become an area of great scientific interest. Over the past 15 years a few specific VATP...