The influence of membrane lipid structure on plasma membrane Ca2+ -ATPase activity.
Lipid composition and Ca(2+)-ATPase activity both change with age and disease in many tissues. We explored relationships between lipid composition/structure and plasma membrane Ca(2+)-ATPase (PMCA) activity. PMCA was purified from human erythrocytes and was reconstituted into liposomes prepared from human ocular lens membrane lipids and synthetic lipids. Lens lipids were used in this study as a model for naturally ordered lipids, but the influence of lens lipids on PMCA function is especially relevant to the lens since calcium homeostasis is vital to lens clarity. Compared to fiber cell lipids, epithelial lipids exhibited an ordered to disordered phase transition temperature that was 12 degrees C lower. Reconstitution of PMCA into lipids was essential for maximal activity. PMCA activity was two to three times higher when the surrounding phosphatidylcholine molecules contained acyl chains that were ordered (stiff) compared to disordered (fluid) acyl chains. In a completely ordered lipid hydrocarbon chain environment, PMCA associates more strongly with the acidic lipid phosphatidylserine in comparison to phosphatidylcholine. PMCA associates much more strongly with phosphatidylcholine containing disordered hydrocarbon chains than ordered hydrocarbon chains. PMCA activity is influenced by membrane lipid composition and structure. The naturally high degree of lipid order in plasma membranes such as those found in the human lens may serve to support PMCA activity. The absence of PMCA activity in the cortical region of human lenses is apparently not due to a different lipid environment. Changes in lipid composition such as those observed with age or disease could potentially influence PMCA function.
Tang
Daxin
D
Department of Ophthalmology and Visual Science, University of Louisville School of Medicine, KY 40202, USA.
Dean
William L
WL
Borchman
Douglas
D
Paterson
Christopher A
CA
D000293:Adolescent; D000328:Adult; D000368:Aged; D000252:Calcium-Transporting ATPases / Q000737:chemistry* / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000737:chemistry / Q000378:metabolism; D002648:Child; D002675:Child, Preschool; D004910:Erythrocyte Membrane / Q000201:enzymology*; D031541:Fluorescence Resonance Energy Transfer; D006801:Humans; D007908:Lens, Crystalline / Q000737:chemistry; D008081:Liposomes; D008563:Membrane Lipids / Q000737:chemistry*; D008875:Middle Aged; D044367:Phase Transition; D010743:Phospholipids / Q000737:chemistry; D053499:Plasma Membrane Calcium-Transporting ATPases
D027682:Cation Transport Proteins; D008081:Liposomes; D008563:Membrane Lipids; D010743:Phospholipids; C507517:ATP2B4 protein, human; D053499:Plasma Membrane Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases