Effects of phosphatidylethanolamines on the activity of the Ca2+-ATPase of sarcoplasmic reticulum

Abstract

ATPase activities for the Ca(2+)-ATPase of skeletal muscle sarcoplasmic reticulum reconstituted into dioleoylphosphatidylethanolamine [di(C18:1)PE] are, at temperatures higher than 20 degrees C, lower than in dioleoylphosphatidylcholine [di(C18:1)PC], whereas in egg yolk phosphatidylethanolamine the activities are the same as in di(C18:1)PC up to 25 degrees C, suggesting that low ATPase activities occur when the phosphatidylethanol-amine species is in the hexagonal H11 phase. ATPase activities measured in mixtures of di(C18:1)PC and di(C18:1)PE do not change with changing di(C18:1)PE content up to 80%. It is concluded that curvature frustration in bilayers containing di(C18:1)PE has no effect on ATPase activity. The rates of phosphorylation and of Ca2+ transport are identical for the native ATPase and for the ATPase in di(C18:1)PE. Dephosphorylation of the phosphorylated ATPase in di(C18:1)PE at 25 degrees C is, however, slower than for the native ATPase, explaining the lower steady-state rate of ATP hydrolysis; in egg yolk phosphatidylethanolamine at 25 degrees C the rate of dephosphorylation is equal to that for the unreconstituted ATPase. Phosphorylation of the ATPase by P1 in the absence of Ca2+ is unaffected by reconstitution in di(C18:1)RE. The stoichiometry of Ca2+ binding to the ATPase is also unaltered. Studies of the effect of di(C18:1)PE on the fluorescence intensity of the ATPase labelled with 7-chloro-4-nitro-2,1,3-benzoxadiazole are consistent with an increase in the E1/E2 equilibrium constant, where E1 is the conformation of the ATPase with two high-affinity binding sites for Ca2+ exposed to the cytoplasm, and E2 is a conformation unable to bind cytoplasmic Ca2+. A slight increase in affinity for Ca2+ can be attributed to the observed increase in the E1/E2 equilibrium constant.

Role of lipid polymorphism in G protein-membrane interactions: Nonlamellar-prone phospholipids and peripheral protein binding to membranes

“…Moreover, the transient presence of such H II phases or other membrane defects may contribute to regulate certain cellular events, such as peripheral protein trafficking, exo-endocytic processes, and vesicle fusion͞fission phenomena. Some recent studies support the involvement of nonlamellar structures, rather than the alteration of other physicochemical properties of membranes, in the control of a number of functions: (i) when PEs are induced to adopt the lamellar phase, G proteins and PKC dissociate from brain cortex plasma membranes (16); (ii) the binding of the insect peripheral protein apolipophorin III to model membranes also appears to be favored by the presence of H II structures (9); (iii) PE species with lower hexagonal phase transition temperature (T H ) values also induce greater increases in G protein binding (this work) and in the PKC activity and binding to membranes (20); and (iv) PEs in the hexagonal phase, but not in the lamellar phase, are able to modulate the Ca 2ϩ -ATPase activity (8). The present study documents an important role of hexagonal-prone lipids (and possibly of H II propensity or H II structures) for signal transduction and other cellular events involving peripheral proteins whose interaction with membranes is regulated by nonlamellar-prone lipids.…”

“…Moreover, PEs with lower lamellar to hexagonal (H II ) phase transition temperature were more effective in increasing this binding, indicating that the presence or propensity to form such nonlamellar structures may play an important role in the G protein association with membranes. Nonlamellar (H II ) lipid structures are required for fusion and fission of lipid vesicles (6,7) and for the activity of certain enzymes (8), but, in general terms, the reason these lipid species are so abundant in natural membranes remains unclear. Interestingly, this mechanism affects not only G proteins, but also other unrelated proteins [protein kinase C (PKC) and the insect peripheral protein apolipophorin III] (9).…”

Effects of oleic acid and its congeners, elaidic and stearic acids, on the structural properties of phosphatidylethanolamine membranes

“…Here, it has been shown that OA modulated the membrane structure, inducing negative membrane curvature strain (H II -phase facilitation) on PE lipids, whereas the closely related FAs, EA and SA, did not alter markedly the phospholipid bilayer and H II properties. Because the plasma membrane structure regulates a wide variety of cell functions (see above), the present results are relevant to understanding the relationship between membrane structure and function (e.g., 8,24,25).…”

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

“…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.…”