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Objectives— The aim of this study was to determine the role of ATP binding cassette transporter A1 (ABCA1) on generation of different-sized nascent HDLs.Methods and Results— HEK293 cells stably-transfected with ABCA1 (HEK293-ABCA1) or non-transfected (control) cells were incubated with lipid free125 I-apoA-I for 24 hours. Incubation of apoA-I with HEK293-ABCA1 cells, but not control cells, led to the formation of heterogeneous-sized, pre-β migrating nascent HDL subpopulations (pre-β1 to -4) that varied in size (7.1 to 15.7 nm), lipid, and apoA-I content. Kinetic studies suggested that all subpopulations were formed simultaneously, with no evidence for a precursor-product relationship between smaller and larger-sized particles. When isolated nascent pre-β HDLs (pre-β1 to -4) were added back to HEK293-ABCA1 cells, their ability to bind to ABCA1 and efflux lipid was severely compromised. Heat-denaturation of pre-β1 HDL resulted in partial recovery of ABCA1 binding, suggesting that initial interaction of apoA-I with ABCA1 results in a constrained conformation of apoA-I that decreases subsequent binding.Conclusions— Interaction of apoA-I with ABCA1 results in the simultaneous generation of pre-β HDLs of discrete size and chemical composition. These nascent particles are poor substrates for subsequent lipidation by ABCA1 and presumably require additional non-ABCA1-mediated lipidation for further maturation.

Minimal Lipidation of Pre-β HDL by ABCA1 Results in Reduced Ability to Interact with ABCA1