Characterization and analysis of conserved motifs in a peroxisomal ATP-binding cassette transporter

The adrenoleukodystrophy protein (ALDP) and the 70-kDa peroxisomal membrane protein are half ATP-binding cassette (ABC) transporters in the human peroxisome membrane. Both are implicated in genetic disorders of peroxisome biogenesis and function. Proteins homologous to ALDP and the 70-kDa peroxisomal membrane protein have been discovered in other eukaryotic organisms and form a growing group of peroxisomal half ABC transporters. Amino acid sequence alignment of these and other ABC transporters reveals several protein motifs that are highly conserved both in sequence and location. Here we characterize two of these, designated the EAA-like and the loopl motifs. We study them by introducing missense mutations in Pxalp, a Saccharomyces cerevisiae ortholog of ALDP, and show that both motifs are important for Pxalp function. Interestingly, missense mutations in corresponding amino acids in ALDP cause adrenoleukodystrophy in humans. We conclude that these motifs are important for ABC transporter function and that the yeast protein Pxalp is a useful system, for understanding the molecular basis of adrenoleukodystrophy.