Which transporter pumps free cholesterol to lipid-poor HDL to form nascent pre-B HDL?

• A. ABCA-1 Transporter
• B. ABCG-1 Transporter
• C. SR-B1 Receptor
• D. LDL Receptor

Answer: (A)

Cholesterol efflux to lipid-poor apolipoprotein A-I to form nascent HDL is driven by the ABCA1 transporter. ABCA1 is an ATP-binding cassette transporter that uses ATP hydrolysis to move cholesterol and phospholipids from cells to lipid-poor ApoA-I, generating discoidal nascent (pre‑beta) HDL particles. This step is essential for HDL biogenesis and explains why ABCA1 is the correct mediator.

Other proteins play different roles. ABCG1 mainly facilitates cholesterol efflux to mature HDL particles rather than to ApoA-I to form nascent HDL. SR-B1 acts as a receptor that mediates selective uptake of cholesteryl esters from HDL into cells, with bidirectional flux possible, rather than initiating nascent HDL formation. LDL receptor binds LDL particles and mediates their uptake, not HDL formation.