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J Biol Chem. 2017 Jul 14;292(28):11980-11991. doi: 10.1074/jbc.M117.784819. Epub 2017 Jun 1.

Clinical or ATPase domain mutations in ABCD4 disrupt the interaction between the vitamin B12-trafficking proteins ABCD4 and LMBD1.

Author information

1
From the Division of Metabolism and Children's Research Center, University Children's Hospital, CH-8032 Zurich, Switzerland.
2
Neurophotonics Laboratory UMR 8250, Paris Descartes University, CNRS, Sorbonne Paris Cité, F-75006 Paris, France.
3
UMR-S UL-INSERM U954 Nutrition-Genetics-Environmental Risk Exposure and Reference Centre of Inborn Metabolism Diseases, Medical Faculty of Nancy University and University Hospital Centre, Nancy, France.
4
Nutrition and Metabolism Unit, Queen Fabiola Children's University Hospital, Free University of Brussels (ULB), 1020 Brussels, Belgium.
5
CBMIT team, UMR 8601, Paris Descartes University, CNRS, Sorbonne Paris Cité, F-75006 Paris, France.
6
Department of Oncology, Children's Research Center, University Children's Hospital, CH-8032 Zurich, Switzerland.
7
From the Division of Metabolism and Children's Research Center, University Children's Hospital, CH-8032 Zurich, Switzerland, sean.froese@kispi.uzh.ch.
8
Rare Disease Initiative Zurich (radiz), Clinical Research Priority Program for Rare Diseases, University of Zurich, CH-8006 Zurich, Switzerland, and.
9
From the Division of Metabolism and Children's Research Center, University Children's Hospital, CH-8032 Zurich, Switzerland, matthias.baumgartner@kispi.uzh.ch.
10
Zurich Center for Integrative Human Physiology, University of Zurich, CH-8006 Zurich, Switzerland.

Abstract

Vitamin B12 (cobalamin (Cbl)), in the cofactor forms methyl-Cbl and adenosyl-Cbl, is required for the function of the essential enzymes methionine synthase and methylmalonyl-CoA mutase, respectively. Cbl enters mammalian cells by receptor-mediated endocytosis of protein-bound Cbl followed by lysosomal export of free Cbl to the cytosol and further processing to these cofactor forms. The integral membrane proteins LMBD1 and ABCD4 are required for lysosomal release of Cbl, and mutations in the genes LMBRD1 and ABCD4 result in the cobalamin metabolism disorders cblF and cblJ. We report a new (fifth) patient with the cblJ disorder who presented at 7 days of age with poor feeding, hypotonia, methylmalonic aciduria, and elevated plasma homocysteine and harbored the mutations c.1667_1668delAG [p.Glu556Glyfs*27] and c.1295G>A [p.Arg432Gln] in the ABCD4 gene. Cbl cofactor forms are decreased in fibroblasts from this patient but could be rescued by overexpression of either ABCD4 or, unexpectedly, LMBD1. Using a sensitive live-cell FRET assay, we demonstrated selective interaction between ABCD4 and LMBD1 and decreased interaction when ABCD4 harbored the patient mutations p.Arg432Gln or p.Asn141Lys or when artificial mutations disrupted the ATPase domain. Finally, we showed that ABCD4 lysosomal targeting depends on co-expression of, and interaction with, LMBD1. These data broaden the patient and mutation spectrum of cblJ deficiency, establish a sensitive live-cell assay to detect the LMBD1-ABCD4 interaction, and confirm the importance of this interaction for proper intracellular targeting of ABCD4 and cobalamin cofactor synthesis.

KEYWORDS:

ABC transporter; ABCD4; LMBD1; cblF; cblJ; fluorescence resonance energy transfer (FRET); homology modeling; inborn error of metabolism; protein-protein interaction; vitamin B12

PMID:
28572511
PMCID:
PMC5512089
DOI:
10.1074/jbc.M117.784819
[Indexed for MEDLINE]
Free PMC Article

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