ABCMdb

ABCA1 p.Thr1088Ala

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Publications

PMID: 23221702 [PubMed] Tomioka M et al: "The effects of neurological disorder-related codon variations of ABCA13 on the function of the ABC protein."

No. Sentence Comment

1 Here, we examined the effects of neurological disorder-related SNPs ABCA13, T4031A and R4843C in the context of ABCA1, and found that the former SNP (T1088A in ABCA1) severely impaired the ABCA1 functions of apolipoprotein A-I (apoA-I) binding and cholesterol efflux. Login to comment
16 Two SNPs of ABCA13, T4031A and R4843C, were inserted into the corresponding amino acid residues of ABCA1, T1088A and K2031C. Login to comment
66 Hence we established HEK293 cells that stably expressed ABCA1 containing ABCA13 SNPs, ABCA1-T1088A, ABCA1- K2031C, and ABCA1-K2031R (as control). Login to comment
69 When the cells were incubated with a physiological concentration of apoA-I (10 mg/mL) for 24 h, a significant amount of cholesterol was transported from them to the medium by ABCA1 (Fig. 2A), but we found that ABCA1-MM did not mediate apoA-I-dependent cholesterol efflux, and that W590S Tangier mutation reduced cholesterol efflux by about 55%, as reported previously.12) Furthermore, the T1088A SNP drastically reduced cholesterol efflux, by about 90%. Login to comment
70 However, the K2031C SNP did not significantly affect cholesterol efflux as compared to the wild type or K2031R (Fig. 2A). Login to comment
71 ApoA-I binding of HEK/ABCA1-SNP mutants at the plasma membrane We have reported that the first step in high-density lipoprotein (HDL) formation is apoA-I binding to the extracellular domains of ABCA1.13) Hence we examined to determine whether the loss in the cholesterol efflux ability of T1088A was due to a change in apoA-I binding. Login to comment
73 W509S retained the ability to interact with apoA-I, while MM abolished that ability, as found previously.10) Furthermore, apoA-I binding was severely reduced (by 76%) by the T1088A SNP, while K2031C showed only a mild reduction (44%) (Fig. 2B). Login to comment
74 These results suggest that HEK/ABCA1-T1088A has low apoA-I-binding activity. Login to comment
75 Total and surface expression of the ABCA1-SNP mutants The fluorescence intensity of the GFP that fused to the C-terminus of ABCA1 suggests that T1088A did not severely impair total expression as compared to the wild-type ABCA1 (Fig. 2B), but it was difficult to compare surface expression because ABCA1 also located to the intracellular vesicles.14) Hence we examined the relative surface expression of ABCA1 by biotinylating cell-surface proteins. Login to comment
76 The total expression of T1088A was similar to that of the wild-type and the other mutants, with the exception of W590S (Fig. 3A). Login to comment
77 However, the amount of biotinylated ABCA1-T1088A was low as compared with the other mutants, and the fraction of surface localization was reduced by about 70% as compared to ABCA1-MM (Fig. 3B). Login to comment
78 To confirm this change in the subcellular localization of ABCA1-T1088A, we examined glycosylation via EndoH, which cleaves within the chitobiose core of high mannose-type N-linked oligosaccharides, and PNGaseF, which cleaves all types of N-linked oligosaccharides. Login to comment
79 For K2031C and wild-type K2031R, most of the protein was resistant to EndoH, but 50% or more of ABCA1-T1088 was sensitive to EndoH (Fig. 4), suggesting that the T1088A mutation caused improper folding of the protein. Login to comment
100 No SNPs have been reported at these positions in ABCA1, although more than 100 coding variants have been identified in ABCA1.15) Using PolyPhen-2, T1088A and K2031C were both predicted to impair the function of ABCA1, with scores of 1.000 and 0.999, respectively,16,17) but the effects of T1088A and K2031C replacement were quite different. Login to comment
101 T1088A severely impaired the subcellular localization and the functions of ABCA1, specifically apoA-I binding and cholesterol efflux, but K2031C showed only a mild effect on apoA-I binding, and no effect on cholesterol efflux. Login to comment
102 Based on the structure of mouse mdr1a,18) T1088A can be mapped at the interface between two NBDs and K2031 at the domain protruding to the outside (Fig. 6). Login to comment
103 The T1088A replacement of a hydrophilic by a hydrophobic amino acid might change the environment around its side chain and affect protein folding. Login to comment
104 Biotinylation of surface proteins and glycosylation analysis suggested that some fraction of ABCA1-T1088A reached the plasma membrane. Login to comment
67 Hence we established HEK293 cells that stably expressed ABCA1 containing ABCA13 SNPs, ABCA1-T1088A, ABCA1- K2031C, and ABCA1-K2031R (as control). Login to comment
72 ApoA-I binding of HEK/ABCA1-SNP mutants at the plasma membrane We have reported that the first step in high-density lipoprotein (HDL) formation is apoA-I binding to the extracellular domains of ABCA1.13) Hence we examined to determine whether the loss in the cholesterol efflux ability of T1088A was due to a change in apoA-I binding. Login to comment
80 For K2031C and wild-type K2031R, most of the protein was resistant to EndoH, but 50% or more of ABCA1-T1088 was sensitive to EndoH (Fig. 4), suggesting that the T1088A mutation caused improper folding of the protein. Login to comment
105 Biotinylation of surface proteins and glycosylation analysis suggested that some fraction of ABCA1-T1088A reached the plasma membrane. Login to comment