ABCD1, also known as adrenoleukodystrophy protein (ALDP), is a member of the ATP-binding cassette (ABC) transporter superfamily. ALDP is a multi-pass membrane protein and localized at peroxisome membrane. Various mutations of ABCD1 gene cause X-linked adrenoleukodystrophy (X-ALD), an inherited neurodegenerative disease affecting the nervous system white matter and adrenal cortex. It results in mental deterioration, corticospinal tract dysfunction, and cortical blindness. ALDP is supposed to function as a homodimer allowing the entry of CoA-esters of very-long chain fatty acids into the peroxisome, the unique site of their β-oxidation. However, the defined function of ALDP has not been well investigated so far.