An amphitropic cAMP-binding protein in yeast mitochondria

ABSTRACT: We describe the first example of a mitochondrial protein with a covalently attached phos-phatidylinositol moiety acting as a membrane anchor. The protein can be metabolically labeled with both stearic acid and inositol. The stearic acid label is removed by phospholipase D whereupon the protein with the retained inositol label is released from the membrane. This protein is a cAMP receptor of the yeast Saccharomyces cereuisiae and tightly associated with the inner mitochondrial membrane. However, it is converted into a soluble form during incubation of isolated mitochondria with Ca2+ and phospholipid (or lipid derivatives). This transition requires the action of a proteinaceous, N-ethylmaleimide-sensitive component of the intermembrane space and is accompanied by a decrease in the lipophilicity of the cAMP receptor. We propose that the component of the intermembrane space triggers the amphitropic behavior of the mitochondrial lipid-modified CAMP-binding protein through a phospholipase activity. Only in recent years specific fatty acids have been recog-nized to play important roles in the association of proteins with membranes. Both noncovalent and covalent interactions be-tween fatty acids and proteins have been reported. Among the latter are GTP-binding proteins (Molenaar et al., 1988)

Stimulation of cell surface F1-ATPase activity by apolipoprotein A-I inhibits endothelial cell apoptosis and promotes proliferation

OBJECTIVES - Several findings argue for a protective effect of high-density lipoproteins (HDLs) against endothelial dysfunction. The molecular mechanisms underlying this protective effect are not fully understood, although recent works suggest that the actions of HDL on the endothelium are initiated by multiple interactions between HDLs (lipid or protein moiety) and cell surface receptors. We previously showed that the mitochondrial related F1-ATPase is a cell surface receptor for HDLs and their main atheroprotective apolipoprotein (apoA-I). Herein we test the hypothesis that the cell surface F1-ATPase may contribute to the ability of apoA-I and HDLs to maintain endothelial cell survival. METHODS AND RESULTS - Cell imaging and binding assays confirmed the presence of the F1-ATPase at the surface of human umbilical vein endothelial cells (HUVECs) and its ability to bind apoA-I. Cell surface F1-ATPase activity (ATP hydrolysis into ADP) was stimulated by apoA-I and was inhibited by its specific inhibitor IF1-H49K. Furthermore the antiapoptotic and proliferative effects of apoA-I on HUVECs were totally blocked by the F1-ATPase ligands IF1-H49K, angiostatin and anti-βF1-ATPase antibody, independently of the scavenger receptor SR-BI and ABCA1. CONCLUSION - This study suggests an important contribution of cell surface F1-ATPase to apoA-I-mediated endothelial cell survival, which may contribute to the atheroprotective functions of apoA-I. © 2009 American Heart Association, Inc