ABCB4 is described as an ATP-binding cassette (ABC) transporter that primarily transports lipids of the phosphatidylcholine (PC) family but is also capable of translocating a subset of typical multidrug-resistance-associated drugs. The high degree of amino acid identity of 76% for ABCB4 and ABCB1, which is a prototype multidrug-resistance-mediating protein, results in ABCB4's second subset of substrates, which overlap with ABCB1's substrates. This often leads to incomplete annotations of ABCB4, in which it was described as exclusively PC-lipid specific. When the hydrophilic amino acids from ABCB4 are changed to the analogous but hydrophobic ones from ABCB1, the stimulation of ATPase activity by 1,2-dioleoyl-sn-glycero-3-phosphocholine, as a prime example of PC lipids, is strongly diminished, whereas the modulation capability of ABCB1 substrates remains unchanged. This indicates two distinct and autonomous substrate binding sites in ABCB4.

ABCB4 被描述为一种 ATP 结合盒 (ABC) 转运蛋白，主要转运磷脂酰胆碱 (PC) 家族的脂质，但也能够转运典型的多药耐药相关药物的子集。ABCB4 和 ABCB1 具有 76% 的高度氨基酸同一性，这是一种原型多药耐药介导蛋白，导致 ABCB4 的第二个底物子集与 ABCB1 的底物重叠。这通常会导致 ABCB4 的注释不完整，其中它被描述为专门针对 PC 脂质。当来自 ABCB4 的亲水氨基酸变为来自 ABCB1 的类似但疏水的氨基酸时，1,2-二油酰-sn对 ATP 酶活性的刺激-glycero-3-phosphocholine，作为 PC 脂质的主要例子，强烈减少，而 ABCB1 底物的调节能力保持不变。这表明 ABCB4 中有两个不同的自主底物结合位点。