Conservation of targeting but divergence in function and quality control of peroxisomal ABC transporters: an analysis using cross-kingdom expression

Abstract

ABC (ATP-binding cassette) subfamily D transporters are found in all eukaryotic kingdoms and are known to play essential roles in mammals and plants; however, their number, organization and physiological contexts differ. Via cross-kingdom expression experiments, we have explored the conservation of targeting, protein stability and function between mammalian and plant ABCD transporters. When expressed in tobacco epidermal cells, the mammalian ABCD proteins ALDP (adrenoleukodystrophy protein), ALDR (adrenoleukodystrophy-related protein) and PMP70 (70 kDa peroxisomal membrane protein) targeted faithfully to peroxisomes and P70R (PMP70-related protein) targeted to the ER (endoplasmic reticulum), as in the native host. The Arabidopsis thaliana peroxin AtPex19_1 interacted with human peroxisomal ABC transporters both in vivo and in vitro, providing an explanation for the fidelity of targeting. The fate of X-linked adrenoleukodystrophy disease-related mutants differed between fibroblasts and plant cells. In fibroblasts, levels of ALDP in some 'protein-absent' mutants were increased by lowtemperature culture, in some cases restoring function. In contrast, all mutant ALDP proteins examined were stable and correctly targeted in plant cells, regardless of their fate in fibroblasts. ALDR complemented the seed germination defect of the Arabidopsis cts-1 mutant which lacks the peroxisomal ABCD transporter CTS (Comatose), but neither ALDR nor ALDP was able to rescue the defect in fatty acid β-oxidation in establishing seedlings. Taken together, our results indicate that the mechanism for trafficking of peroxisomal membrane proteins is shared between plants and mammals, but suggest differences in the sensing and turnover of mutant ABC transporter proteins and differences in substrate specificity and/or function.

Adrenoleukodystrophy – neuroendocrine pathogenesis and redefinition of natural history

“…Although ALDP is an integral peroxisome membrane protein, 65% of missense mutations affect protein folding and stability, which results in a marked reduction of ALDP from the membrane 106,107 . Some of these 'unstable' mutants can be rescued by low temperature culture of fibroblasts, which in some cases normalizes VLCFA levels 108 . Studies aimed at the identification of small-molecules that correct aberrant protein folding might, therefore, have therapeutic relevance for ALD.…”

X-linked Adrenoleukodystrophy

“…This involvement in fatty acid metabolism contributes to the mobilization of storage triacylglycerol and to the turn over of membrane lipids [201,202,208,209]. Recently, very interesting complementation experiments of the At_ABCD1 plant mutant with the human ABCD1 and ABCD2 proteins have been performed [212]. Recently, very interesting complementation experiments of the At_ABCD1 plant mutant with the human ABCD1 and ABCD2 proteins have been performed [212].…”

“…Of note, ABCD1 protein was still detected in 2 patients harboring in-frame deletion/insertion mutations (Lys665delinsGlu and Val635delinsAlaMet) [229] and one patient presenting a micro deletion (Phe175del) [230]. Interestingly, the rescue of mutations that result in mistargeting or instability is possible and opens another field for therapeutic intervention targeting the quality control machinery [212]. Up to 58 % of them resulted in unstable and absent levels of ABCD1, 11% resulted in strongly reduced expression levels, and 31% of them did not affect the ABCD1 expression levels.…”

Barley has two peroxisomal ABC transporters with multiple functions in β-oxidation

“…Thus, it appears that plants have apparently evolved a broad specificity peroxisomal ABC transporter to mediate the import of the wide range of substrates that they need to process by β-oxidation (Baker et al , 2006). This is in contrast to mammalian and yeast peroxisomal ABC transporters which exhibit restricted substrate selectivities as judged by cross-kingdom complementation experiments and characterization in yeast and in vivo (van Roermund et al, 2008, 2011, 2014; Zhang et al , 2011). …”