Lipid dynamics in discoidal lipoprotein complexes of apolipoprotein A-I

PRIETO ED; OLIVIERA T; LAMY T; GARDA HA

San Carlos de Bariloche

Congreso; XXXII Reunión Anual de SAB y XXXIX Reunión Anual de SAIB; 2003

SAB - SAIB

Fiscoidal high density lipoprotein complexes (dHDL) of apolipoprotein AI (apoAI) are intermediates in HDL metabolism and reverse cholesterol transport. Although dHDL formation ?in vivo? requires the assistance of cellular proteins, they can be obtained ?in vitro? by mixing apoAI with vesicles of zwitterionic phospholipids at the gel to liquid-crystalline phase transition temperature (Tt). several models for dHDL were proposed which differ in the arrangement of apoAI helices, but all of them agree that the protein is wrapped around the edge of a phospholipid bilayer. in this work, we used electronic paramagnetic resonance (EPR) to obtain information about how the dynamics of disc lipids is affected by apoAI. different spin-labeled phospholipids probes reporting the mobility at different bilayer regions were used:TEMPO-PC (with label in the polar head) as well as 5- and 16-doxyl PCs (with label in the hydrocarbon chain). results show that above Tt, apoAI discs have a decreased hydrocarbon chain mobility (reported by 5- and 16-doxyl PCs) and an increased mobility of polar head groups (sensed by TEMPO-PC) compared with protein-free bilayers. the opposite effect of apoAI is observed below Tt. these results are typical for proteins inserted or spanning the bilayer and are discussed taking into account the proposed models for dHDLin vivo? requires the assistance of cellular proteins, they can be obtained ?in vitro? by mixing apoAI with vesicles of zwitterionic phospholipids at the gel to liquid-crystalline phase transition temperature (Tt). several models for dHDL were proposed which differ in the arrangement of apoAI helices, but all of them agree that the protein is wrapped around the edge of a phospholipid bilayer. in this work, we used electronic paramagnetic resonance (EPR) to obtain information about how the dynamics of disc lipids is affected by apoAI. different spin-labeled phospholipids probes reporting the mobility at different bilayer regions were used:TEMPO-PC (with label in the polar head) as well as 5- and 16-doxyl PCs (with label in the hydrocarbon chain). results show that above Tt, apoAI discs have a decreased hydrocarbon chain mobility (reported by 5- and 16-doxyl PCs) and an increased mobility of polar head groups (sensed by TEMPO-PC) compared with protein-free bilayers. the opposite effect of apoAI is observed below Tt. these results are typical for proteins inserted or spanning the bilayer and are discussed taking into account the proposed models for dHDL