Effect of propensity of hexagonal II phase formation on the activity of mitochondrial ubiquinol-cytochrome c reductase and H+-ATPase

159

121

The apoptotic protein tBid is effective in promoting both leakage and lipid mixing in liposomes composed of cardiolipin and phosphatidylcholine at a molar ratio of 1:2 in the presence of calcium. When half of the phosphatidylcholine component of these liposomes is replaced with phosphatidylethanolamine, a lipid that promotes negative membrane curvature, the rates of both leakage and lipid mixing caused by tBid are substantially increased. Replacement of cardiolipin with phosphatidylglycerol, a lipid that is structurally similar to cardiolipin but does not promote negative membrane curvature in the presence of calcium, prevents the tBid from promoting leakage. The promotion of leakage by tBid is also inhibited by several substances that promote positive membrane curvature, including lysophosphatidylcholine, tritrpticin, a potent antimicrobial peptide, and cyclosporin A, a known inhibitor of cytochrome c release from mitochondria. We directly measured the effect of tBid on membrane curvature by 31 P NMR. We found that tBid promotes the formation of highly curved non-lamellar phases. All of these data are consistent with the hypothesis that tBid promotes negative curvature, and as a result it destabilizes bilayer membranes. Bcl-X L inhibits leakage and lipid mixing induced by tBid. Bcl-X L is anti-apoptotic. It reduces the promotion of non-bilayer phases by tBid, although by itself Bcl-X L is capable of promoting their formation. Bcl-X L has little effect on liposomal integrity. Our results suggest that the anti-apoptotic activity of Bcl-X L is not a consequence of its interaction with membranes, but rather with other proteins, such as tBid.

mentioning

confidence: 99%

The Apoptotic Protein tBid Promotes Leakage by Altering Membrane Curvature

Epand

Martinou

Fornallaz-Mulhauser

et al. 2002

159

121

“…Also, it was shown that nonlamellar lipid structure is induced by signal peptides (16). In particular, such activities as the ATP exchange by mitochondrial proteins (17) and Ca 2ϩ -ATPase activity increase with increasing PE content (18), suggesting importance of nonlamellar structure.…”

mentioning

confidence: 99%

Effects of Nonlamellar-prone Lipids on the ATPase Activity of SecA Bound to Model Membranes

Ahn

Kim

1998

The effect of nonlamellar-prone lipids, diacylglycerol (DG) and phosphatidylethanolamine (PE), on the ATPase activity of SecA was examined. When Escherichia coli PE of the standard vesicles composed of 60 mol% of this lipid and 40 mol% of dioleoylphosphatidylglycerol (DOPG) is gradually replaced with either dioleoylglycerol (DOG) or dioeloyl PE (DOPE), the ATPase activity of SecA present together increased appreciably. On the other hand, when E. coli PE of the standard vesicles was replaced with DOG analogs, the SecA ATPase activity decreased slightly, and when replaced with phosphatidylcholine the decrease in the ATPase activity was more appreciable. When DOPE or E. coli PE was added to PC vesicles, the SecA ATPase activity was enhanced only slightly, suggesting that the hexagonal II structure per se is not

“…Protein translocation across the E. coli inner membrane lacking PE could be restored by (C18:1)PE (non-lamellar) but not (C14: 0)PE or (C18:1)PC (both lamellar) (32). (18:1⌬9cis)PE (nonlamellar) but not (18:1⌬9trans)PE (lamellar) significantly enhanced the respiratory control ratio of ubiquinol-cytochrome c reductase and ATP-induced membrane potential of the H ϩ -ATPase (33). The photochemical function of rhodopsin (34) and the ATPase activity of E. coli SecA protein (50) are enhanced by non-lamellar PE derivatives.…”

Section: Discussionmentioning

confidence: 95%

Phospholipid-assisted Refolding of an Integral Membrane Protein

Bogdanov¹,

Umeda²,

Dowhan³

1999

126

Escherichia coli-derived phosphatidylethanolamine (PE) or PE with fully saturated fatty acids was able to correct in vitro a defect in folding in the lipid-dependent epitope 4B1 of lactose permease (LacY) resulting from in vivo assembly in the absence of PE. PE plasmalogen, PE with two unsaturated fatty acids, and lyso-PE, which all do not favor bilayer organization, did not support proper refolding. Proper refolding occurred when these latter lipids were mixed with a bilayer-forming lipid (phosphatidylglycerol), which alone could not support refolding. L-Phosphatidylserine (PS; natural diastereomer) did support proper refolding. PE derivatives of increasing degrees of methylation were progressively less effective in supporting refolding, with phosphatidylcholine being completely ineffective. Therefore, the properties of nonmethylated aminophospholipids capable of organization into a bilayer configuration are essential for the recovery of the native state of epitope 4B1 after misassembly in vivo in the absence of PE. How a polytopic membrane protein inserts into the membrane and adopts its native conformation remains one of the major unresolved questions of biology. During membrane assembly, integral membrane proteins must interact with other proteins and with the lipid bilayer itself, resulting in their proper conformational maturation. The role phospholipids play in forming a membrane bilayer and a hydrophobic environment for membrane protein folding and assembly is well accepted (1, 2); however, the role specific phospholipids play in assisting or directing folding of membrane proteins has not been extensively explored. In order to determine the role that individual phospholipids play in the folding of membrane proteins in Escherichia coli, we are using the lactose permease (LacY) 1 as a model system. LacY is one of the most intensively studied integral membrane proteins for which there is both extensive structural information (3, 4) and monoclonal antibodies (mAbs) directed against several extramembrane epitopes whose recognition depends on secondary or tertiary structural organization (5, 6). The organization of extramembrane and transmembrane domains of LacY is characteristic of the major facilitator superfamily of transport proteins (7), making results obtained from studies on LacY applicable to a variety of other transport proteins.Employing a novel blotting technique (Eastern-Western) in which proteins are exposed to phospholipids bound to a solid support during renaturation from SDS in the standard Western blotting procedure, we previously presented the following experimental evidence (8, 9) that the phospholipid phosphatidylethanolamine (PE) acts as a non-protein molecular chaperone in the folding of LacY: (i) LacY appears to fold in vivo with the assistance of PE as assessed by recognition by a conformation-sensitive mAb directed against periplasmic loop P7 (Phe 242 -Gly 254 ), which is flanged by transmembrane domains VII and VIII and defines epitope 4B1 (Fig. 1); (ii) LacY assembled initially in vi...