ABCMdb

ABCB4 p.Gln1118Ala

Predicted by SNAP2:	A: D (59%), C: N (57%), D: D (75%), E: D (71%), F: D (63%), G: D (63%), H: N (93%), I: D (66%), K: N (66%), L: D (66%), M: D (59%), N: N (53%), P: D (80%), R: N (57%), S: D (53%), T: D (63%), V: D (63%), W: D (75%), Y: D (59%),
Predicted by PROVEAN:	A: D, C: D, D: D, E: N, F: D, G: D, H: N, I: D, K: D, L: D, M: D, N: D, P: D, R: D, S: D, T: D, V: D, W: D, Y: D,

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Publications
[hide] Molecular model and ATPase activity of carboxyl-te... Biochemistry (Mosc). 2006;71 Suppl 1:S18-24, 1-2. Qian F, Wei D, Liu J, Yang S
Molecular model and ATPase activity of carboxyl-terminal nucleotide binding domain from human P-glycoprotein.
Biochemistry (Mosc). 2006;71 Suppl 1:S18-24, 1-2., [PMID:16487063]

Abstract [show]
ATP binding and hydrolysis are required for P-glycoprotein mediated multidrug resistance. To investigate the molecular mechanism involved in ATP binding and hydrolysis, a three-dimensional model of the carboxyl-terminal nucleotide binding domain (NBD2) was built by homology modeling. Modeling revealed the human P-glycoprotein ATP-binding site and the possible role of conserved Gln1118 residue. Recombinant NBD2 was overexpressed in Escherichia coli and the conserved Gln1118 residue was mutated to an alanine residue. The Vmax for ATP hydrolysis by the mutant NBD2 was approximately 56% of the Vmax of wild-type NBD2. But both proteins displayed similar affinity for ATP, with Km of 479 and 466 microM for mutant and wild-type NBD2, respectively. These results suggest that the possible role of Gln1118 is as an activating residue for ATP hydrolysis. The molecular model also provided structural information about the interactions between NBD2 and the chemosensitizer quercetin. The complex indicated that quercetin was tightly bound to the ATP-binding site and competed for binding. The three-dimensional model of NBD2 can be used to both guide enzymological studies and provide a theoretical basis for the design of potential multidrug resistance reversers.

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No. Sentence Comment
174 a) ATP dependence of the ATPase activities of the isolated NBD2 (1) and its mutant Q1118A (2). Login to comment
176 b) Lineweaver-Burk plot of dependence of ATPase activity of NBD2 (1) and its mutant Q1118A (2). Login to comment

[hide] The Transmission Interfaces Contribute Asymmetrica... J Biol Chem. 2015 Jul 3;290(27):16954-63. doi: 10.1074/jbc.M115.652602. Epub 2015 May 18. Loo TW, Clarke DM
The Transmission Interfaces Contribute Asymmetrically to the Assembly and Activity of Human P-glycoprotein.
J Biol Chem. 2015 Jul 3;290(27):16954-63. doi: 10.1074/jbc.M115.652602. Epub 2015 May 18., [PMID:25987565]

Abstract [show]
P-glycoprotein (P-gp; ABCB1) is an ABC drug pump that protects us from toxic compounds. It is clinically important because it confers multidrug resistance. The homologous halves of P-gp each contain a transmembrane (TM) domain (TMD) with 6 TM segments followed by a nucleotide-binding domain (NBD). The drug- and ATP-binding sites reside at the interface between the TMDs and NBDs, respectively. Each NBD is connected to the TMDs by a transmission interface involving a pair of intracellular loops (ICLs) that form ball-and-socket joints. P-gp is different from CFTR (ABCC7) in that deleting NBD2 causes misprocessing of only P-gp. Therefore, NBD2 might be critical for stabilizing ICLs 2 and 3 that form a tetrahelix bundle at the NBD2 interface. Here we report that the NBD1 and NBD2 transmission interfaces in P-gp are asymmetric. Point mutations to 25 of 60 ICL2/ICL3 residues at the NBD2 transmission interface severely reduced P-gp assembly while changes to the equivalent residues in ICL1/ICL4 at the NBD1 interface had little effect. The hydrophobic nature at the transmission interfaces was also different. Mutation of Phe-1086 or Tyr-1087 to arginine at the NBD2 socket blocked activity or assembly while the equivalent mutations at the NBD1 socket had only modest effects. The results suggest that the NBD transmission interfaces are asymmetric. In contrast to the ICL2/3-NBD2 interface, the ICL1/4-NBD1 transmission interface is more hydrophilic and insensitive to mutations. Therefore the ICL2/3-NBD2 transmission interface forms a precise hydrophobic connection that acts as a linchpin for assembly and trafficking of P-gp.

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Sentences [show]
No. Sentence Comment
248 A study of Q loop mutations Q475A(NBD1) and Q1118A- (NBD2) suggested that the P-gp transport mechanism shows redundancy (47). Login to comment
249 It was found that the single Q475A or Q1118A mutants retained transport activity and 35-50% of wild-type ATPase activity but the double Q475A/Q1118A mutant was inactive. Login to comment
254 A Q475A/Q1118A control P-gp however, showed little detectable ATPase activity. Login to comment