ABCR expression in foveal cone photoreceptors and its role in Stargardt macular dystrophy

Molday, Laurie L.; Rabin, Arnold R.; Molday, Robert S.

doi:10.1038/77004

Cited by 218 publications

(109 citation statements)

References 13 publications

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“…The matrix was washed two more times with 0.4 ml of column buffer before being transferred to Ultrafree-MC (0.45-m filter) spin column (Millipore). The samples containing the immobilized 1D4-tagged ABCA4 proteins with bound labeled retinoid were washed three more times before extracting the 3 H-labeled all-trans-retinal from the matrix with 0.5 ml of ice-cold ethanol for 15 min at room temperature by centrifugation. Radiolabeled all-trans-retinal in the ethanol extractions was determined by liquid scintillation counting.…”

Section: Methodsmentioning

confidence: 99%

“…ABCA4, also known as ABCR or the rim protein, is a member of the ABCA subfamily of ATP binding cassette transporters expressed in vertebrate photoreceptor cells (1)(2)(3)(4). It is localized along the rims and incisures of rod and cone outer segment discs, where it has been implicated in the binding and transport of the Schiff base adduct of all-trans-retinal and phosphatidylethanolamine (PE) 3 known as N-retinylidene-PE or N-ret-PE across disc membranes as part of visual cycle (3,(5)(6)(7)(8)(9).…”

mentioning

confidence: 99%

“…It is localized along the rims and incisures of rod and cone outer segment discs, where it has been implicated in the binding and transport of the Schiff base adduct of all-trans-retinal and phosphatidylethanolamine (PE) 3 known as N-retinylidene-PE or N-ret-PE across disc membranes as part of visual cycle (3,(5)(6)(7)(8)(9).…”

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confidence: 99%

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Role of the C Terminus of the Photoreceptor ABCA4 Transporter in Protein Folding, Function, and Retinal Degenerative Diseases

Ming¹,

Molday

2009

Journal of Biological Chemistry

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ABCA4 is an ATP-binding cassette transporter that is expressed in rod and cone photoreceptor cells and implicated in the removal of retinal derivatives from outer segments following photoexcitation. Mutations in the ABCA4 gene are responsible for a number of related retinal degenerative diseases, including Stargardt macular degeneration, cone-rod dystrophy, retinitis pigmentosa, and age-related macular degeneration. In order to determine the role of the C terminus of ABCA4 in protein structure and function and understand mechanisms by which C-terminal mutations cause retinal degenerative diseases, we have expressed and purified a series of deletion and substitution mutants of ABCA4 and ABCA1 in HEK 293T cells for analysis of their cellular localization and biochemical properties. Removal of the C-terminal 30 amino acids of ABCA4, including a conserved VFVNFA motif, resulted in a loss in N-retinylidene-phosphatidylethanolamine substrate binding, ATP photoaffinity labeling, and retinal-stimulated ATPase activity. This mutant was also retained in the endoplasmic reticulum of cells. Replacement of the VFVNFA motif with alanine residues also resulted in loss in function and cellular mislocalization. In contrast, C-terminal deletion mutants that retain the VFVNFA motif were functionally active and localized to intracellular vesicles similar to wild-type ABCA4. Our studies indicated that the VFVNFA motif is required for the proper folding of ABCA4 into a functionally active protein. This motif also contributes to the efficient folding of ABCA1 into an active protein. Our results provide a molecular based rationale for the disease phenotype displayed by individuals with mutations in the C terminus of ABCA4.ABCA4, also known as ABCR or the rim protein, is a member of the ABCA subfamily of ATP binding cassette transporters expressed in vertebrate photoreceptor cells (1-4). It is localized along the rims and incisures of rod and cone outer segment discs, where it has been implicated in the binding and transport of the Schiff base adduct of all-trans-retinal and phosphatidylethanolamine (PE) 3 known as N-retinylidene-PE or N-ret-PE across disc membranes as part of visual cycle (3, 5-9).To date, over 500 different mutations in the ABCA4 gene are known to cause Stargardt macular degeneration, an early onset recessive disease characterized by the loss in central vision, the presence of lipofuscin deposits in retinal pigment epithelial cells, a delay in dark adaptation, and progressive degeneration of photoreceptor and retinal pigment epithelial cells (1, 10 -15). Mutations in ABCA4 are also responsible for other related but more severe retinal degenerative diseases, including autosomal recessive cone-rod dystrophy and retinitis pigmentosa (16 -19). Finally, individuals heterozygous for selected diseaselinked mutations in ABCA4 have been suggested to be at higher risk in developing age-related macular degeneration (20). Disease-associated mutations are distributed throughout the ABCA4 gene and comprise missense, splice site, an...

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Section: Methodsmentioning

confidence: 99%

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confidence: 99%

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Role of the C Terminus of the Photoreceptor ABCA4 Transporter in Protein Folding, Function, and Retinal Degenerative Diseases

Ming¹,

Molday

2009

Journal of Biological Chemistry

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“…The Rim 5B4 monoclonal antibody (6) was generated from a mouse immunized with a fusion protein consisting of amino acids 857-1105 of human ABCR in-frame with glutathione S-transferase. The binding site for the Rim 5B4 antibody (LEDTGL-HHK) was determined by epitope mapping using synthetic peptides as previously described (1).…”

Section: Methodsmentioning

confidence: 99%

“…It is localized along the rim region of photoreceptor rod outer segment disc membranes (1,4,5) and more recently has been found in human foveal and peripheral cone outer segments (6). Several studies have implicated ABCR in the retinoid cycle, possibly functioning as a retinal extruder or retinal-phosphatidylethanolamine flippase to facilitate the removal of all-trans-retinal from disc membranes following the photobleaching of rhodopsin (7)(8)(9).…”

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Membrane Topology of the ATP Binding Cassette Transporter ABCR and Its Relationship to ABC1 and Related ABCA Transporters

Bungert¹,

Molday²,

Molday

2001

Journal of Biological Chemistry

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ABCR is a member of the ABCA subclass of ATP binding cassette transporters that is responsible for Stargardt macular disease and implicated in retinal transport across photoreceptor disc membranes. It consists of a single polypeptide chain arranged in two tandem halves, each having a multi-spanning membrane domain followed by a nucleotide binding domain. To delineate between several proposed membrane topological models, we have identified the exocytoplasmic (extracellular/lumen) N-linked glycosylation sites on ABCR. Using trypsin digestion, site-directed mutagenesis, concanavalin A binding, and endoglycosidase digestion, we show that ABCR contains eight glycosylation sites. Four sites reside in a 600-amino acid exocytoplasmic domain of the N-terminal half between the first transmembrane segment H1 and the first multi-spanning membrane domain, and four sites are in a 275-amino acid domain of the C half between transmembrane segment H7 and the second multi-spanning membrane domain. This leads to a model in which each half has a transmembrane segment followed by a large exocytoplasmic domain, a multi-spanning membrane domain, and a nucleotide binding domain. Other ABCA transporters, including ABC1 linked to Tangier disease, are proposed to have a similar membrane topology based on sequence similarity to ABCR. Studies also suggest that the N and C halves of ABCR are linked through disulfide bonds.ABCR, formerly known as the rim protein, is an ATP binding cassette (ABC) 1 transporter found in vertebrate retinal photoreceptor cells (1-3). It is localized along the rim region of photoreceptor rod outer segment disc membranes (1, 4, 5) and more recently has been found in human foveal and peripheral cone outer segments (6). Several studies have implicated ABCR in the retinoid cycle, possibly functioning as a retinal extruder or retinal-phosphatidylethanolamine flippase to facilitate the removal of all-trans-retinal from disc membranes following the photobleaching of rhodopsin (7-9).Mutations in the ABCA4 gene encoding ABCR have been linked to Stargardt disease, a relatively common juvenile macular dystrophy characterized by a decrease in visual acuity, progressive bilateral atrophy of the central retina, and the accumulation of yellow deposits within the retinal pigment epithelial cell layer (2, 10 -13). Mutations in ABCA4 have also been linked to related disease variants, including late-onset fundus flavimaculatus (14), cone-rod dystrophy (15), retinitis pigmentosa-like dystrophy (16, 17), and age-related macular degeneration (18), although the latter remains controversial (19).ABCR is a member of the ABCA subclass of ABC transporters (20). Like most other mammalian ABC transporters, members of this subclass consist of a single long polypeptide chain organized into two tandemly arranged halves. Each half contains a membrane-spanning domain (MSD) followed by a cytoplasmic nucleotide binding domain (NBD). The ABCA subclass is distinguished from other ABC transporter subclasses by the presence of a large domain between the...

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Phenotypic Subtypes of Stargardt Macular Dystrophy–Fundus Flavimaculatus

et al. 2001

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To determine if phenotypic subtypes exist in Stargardt macular dystrophy-fundus flavimaculatus (SMD-FFM). Methods: A cross-sectional study of 63 patients with autosomal recessive SMD-FFM was undertaken. The age of onset, duration of symptoms, visual acuity, and clinical features on fundus examination, color fundus photographs, and fundus autofluorescence images were recorded. Electrophysiological tests, including pattern, focal, and fullfield electroretinogram (ERG), electro-oculogram, and colorcontrast sensitivity measurement, were also performed. Results: Based on electrophysiological attributes (ERG), patients with SMD-FFM could be classified into 3 groups. In group 1, there was severe pattern ERG abnormality with normal scotopic and full-field ERGs. In group 2, there was additional loss of photopic function, and in group 3, there was loss of both photopic and scotopic function. Differences in scotopic or photopic function among groups were not explained on the basis of differences in age of onset or duration of disease. Conclusions: Patients with SMD-FFM can be classified into 3 groups based on the absence or presence of generalized loss of either photopic or photopic and scotopic function. It appears that these 3 groups may represent distinct phenotypic subtypes in SMD-FFM.

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ABCR expression in foveal cone photoreceptors and its role in Stargardt macular dystrophy

Cited by 218 publications

References 13 publications

Role of the C Terminus of the Photoreceptor ABCA4 Transporter in Protein Folding, Function, and Retinal Degenerative Diseases

Role of the C Terminus of the Photoreceptor ABCA4 Transporter in Protein Folding, Function, and Retinal Degenerative Diseases

Membrane Topology of the ATP Binding Cassette Transporter ABCR and Its Relationship to ABC1 and Related ABCA Transporters

Phenotypic Subtypes of Stargardt Macular Dystrophy–Fundus Flavimaculatus

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