CD36 binds oxidized LDL in a mechanism dependent upon fatty acid binding [Membrane Biology]

January 1st, 2015 by Jay, A. G., Chen, A. N., Paz, M. A., Hung, J. P., Hamilton, J. A.

The association of unesterified fatty acid (FA) with the scavenger receptor CD36 has been actively researched, with focuses on FA and oxLDL uptake. CD36 has been shown to bind FA but this interaction has been poorly characterized to date. To gain new insights into the physiological relevance of binding of FA to CD36, we characterized FA binding to the ectodomain of CD36 by the biophysical method surface plasmon resonance (SPR). Five structurally distinct FA (saturated, monounsaturated [cis and trans], polyunsaturated, and oxidized) were pulsed across SPR channels, generating association and dissociation binding curves. Except for the oxidized FA HODE, all FA bound to CD36, with rapid association and dissociation kinetics similar to HSA. Next, to elucidate the role that each FA might play in CD36-mediated oxLDL uptake, we used a fluorescent oxLDL (Dii-oxLDL) live-cell assay with confocal microscopy imaging. CD36-mediated uptake in serum-free media was very low but greatly increased when serum was present. Addition of exogenous FA in serum-free media increased oxLDL binding and uptake to levels found with serum and affected CD36 plasma membrane (PM) distribution. Binding/uptake of oxLDL was dependent upon the FA dose, except for DHA, which exhibited binding to CD36 but did not activate the uptake of oxLDL. HODE also did not affect oxLDL uptake. High affinity FA binding to CD36 and the effects of each FA on oxLDL uptake have important implications for protein conformation, binding of other ligands, functional properties of CD36, and high plasma FA levels in obesity and type2 diabetes.