Mechanistic studies of sterol carrier protein-2 effects on L-cell fibroblast plasma membrane sterol domains.
The factors which regulate intermembrane sterol domains and exchange in biomembranes are not well understood. A new fluorescent sterol exchange assay allowed correlation of changes in polarization to sterol transfer. Analysis of spontaneous sterol exchange between L-cell plasma membranes indicated two exchangeable and one very slowly or nonexchangeable sterol domain. The exchangeable domains exhibited half-times of 23 and 140 min with fractional contributions of 5 and 30%, respectively. Sterol carrier protein-2 (SCP-2) enhanced sterol exchange between L-cell plasma membranes and altered sterol domain size in a concentration dependent manner. Previous model membrane studies indicate that SCP-2 alters sterol domains and exchange through interaction with anionic phospholipids. In contrast to these observations, the ionic shielding agents KCl, low pH, or neomycin were either totally or partially ineffective inhibitors of SCP-2 action in L-cell plasma membrane exchanges. Thus the mechanism of SCP-2 in sterol transfer appears to be less charge dependent in L-cell plasma membranes than in model membranes. The cholesterol lowering drug probucol was also capable of altering the sterol exchange kinetics.
Woodford
J K
JK
Department of Pharmacology and Cell Biophysics, University of Cincinnati Medical Center, OH 45267-0004.
Hapala
I
I
Jefferson
J R
JR
Knittel
J J
JJ
Kavecansky
J
J
Powell
D
D
Scallen
T J
TJ
Schroeder
F
F
D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D005454:Fluorescence Polarization; D006863:Hydrogen-Ion Concentration; D007739:L Cells; D051379:Mice; D008969:Molecular Sequence Data; D009355:Neomycin / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D010940:Plant Proteins; D011189:Potassium Chloride / Q000494:pharmacology; D011341:Probucol / Q000494:pharmacology; D013261:Sterols / Q000378:metabolism*
D002352:Carrier Proteins; D010455:Peptides; D010940:Plant Proteins; D013261:Sterols; C072087:sterol carrier proteins; D011189:Potassium Chloride; D009355:Neomycin; D011341:Probucol