Nucleotide Binding and Nucleotide Hydrolysis Properties of the ABC Transporter MRP6 (ABCC6)
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- 作者：Jie Cai ; Roni Daoud ; Omar Alqawi ; Elias Georges ; Jerry Pelletier ; and Philippe Gros
- 刊名：Biochemistry
- 出版年：2002
- 出版时间：June 25, 2002
- 年：2002
- 卷：41
- 期：25
- 页码：8058 - 8067
- 全文大小：247K
- 年卷期：v.41,no.25(June 25, 2002)
- ISSN：1520-4995
文摘
Mutations in the MRP gene family member MRP6 cause pseudoxanthoma elasticum (PXE) inhumans, a disease affecting elasticity of connective tissues. The normal function of MRP6, including itsphysiological substrate(s), remains unknown. To address these issues, recombinant rat Mrp6 (rMrp6) wasexpressed in the methylotrophic yeast Pichia pastoris. The protein was expressed in the membrane fractionas a stable 170 kDa protein. Its nucleotide binding and hydrolysis properties were investigated using thephotoactive ATP analogue 8-azido-[
-32P]ATP and compared to those of the drug efflux pump MRP1.rMrp6 can bind 8-azido-[-32P]ATP in a Mg2+-dependent and EDTA-sensitive fashion. Co2+, Mn2+, andNi2+ can also support 8-azido-[-32P]ATP binding by rMrp6 while Ca2+, Cd2+, and Zn2+ cannot. Underhydrolysis conditions (at 37 
C), the phosphate analogue beryllium fluoride (BeFx) can stimulate trappingof the 8-azido-[-32P]adenosine nucleotide in rMrp6 (and in MRP1) in a divalent cation-dependent andtemperature-sensitive fashion. This suggests active ATPase activity, followed by trapping and photo-cross-linking of the 8-azido-[-32P]ADP to the protein. By contrast to MRP1, orthovanadate-stimulatednucleotide trapping in rMrp6 does not occur in the presence of Mg2+ but can be detected with Ni2+ ions,suggesting structural and/or functional differences between the two proteins. The rMrp6 protein can bespecifically photolabeled by a fluorescent photoactive drug analogue, [125I]-IAARh123, with characteristicssimilar to those previously reported for MRP1 (1), and this photolabeling of rMrp6 can be modulated byseveral structurally unrelated compounds. The P. pastoris expression system has allowed demonstrationof ATP binding and ATP hydrolysis by rMrp6. In addition to providing large amounts of active proteinfor detailed biochemical studies, this system should also prove useful to identify potential rMrp6 substratesin [125I]-IAARh123 photolabeling competition studies, as well as to study the molecular basis of PXEmutations, which are most often found in the NBD2 of MRP6.
-32P]ATP and compared to those of the drug efflux pump MRP1.rMrp6 can bind 8-azido-[-32P]ATP in a Mg2+-dependent and EDTA-sensitive fashion. Co2+, Mn2+, andNi2+ can also support 8-azido-[-32P]ATP binding by rMrp6 while Ca2+, Cd2+, and Zn2+ cannot. Underhydrolysis conditions (at 37 C), the phosphate analogue beryllium fluoride (BeFx) can stimulate trappingof the 8-azido-[-32P]adenosine nucleotide in rMrp6 (and in MRP1) in a divalent cation-dependent andtemperature-sensitive fashion. This suggests active ATPase activity, followed by trapping and photo-cross-linking of the 8-azido-[-32P]ADP to the protein. By contrast to MRP1, orthovanadate-stimulatednucleotide trapping in rMrp6 does not occur in the presence of Mg2+ but can be detected with Ni2+ ions,suggesting structural and/or functional differences between the two proteins. The rMrp6 protein can bespecifically photolabeled by a fluorescent photoactive drug analogue, [125I]-IAARh123, with characteristicssimilar to those previously reported for MRP1 (1), and this photolabeling of rMrp6 can be modulated byseveral structurally unrelated compounds. The P. pastoris expression system has allowed demonstrationof ATP binding and ATP hydrolysis by rMrp6. In addition to providing large amounts of active proteinfor detailed biochemical studies, this system should also prove useful to identify potential rMrp6 substratesin [125I]-IAARh123 photolabeling competition studies, as well as to study the molecular basis of PXEmutations, which are most often found in the NBD2 of MRP6.