ABCMdb

PMID: 17027309

Li YF, Polgar O, Okada M, Esser L, Bates SE, Xia D
Towards understanding the mechanism of action of the multidrug resistance-linked half-ABC transporter ABCG2: a molecular modeling study.
J Mol Graph Model. 2007 Mar;25(6):837-51. Epub 2006 Aug 30., [PubMed]

Sentences

No. Mutations Sentence Comment

109 ABCG2 p.Lys86Ile ABCG2 p.Thr82Ala ABCG2 p.Lys86Met Mutations T82A, K86M, and K86I [42,43] are part of the Walker A motif; all lead to loss of transport activity. Login to comment 110 ABCG2 p.Thr82Ala The T82A mutation results in the possible loss of interaction with residue R193 in the neighboring LSGGQ motif, potentially affecting dimer assembly. Login to comment 111 ABCG2 p.Lys86Ile ABCG2 p.Lys86Met The K86M or the K86I mutation leads to loss of interaction with the tri-phosphate group of the bound ATP, and thus inactivates the enzyme. Login to comment 112 ABCG2 p.Gln141Lys Q141K, a SNP [22,23], is located on the surface of the small sub-domain near the conserved H3 helix Y.-F Li et al. / Journal of Molecular Graphics and Modelling 25 (2007) 837-851 841 Table 1 Sequence identity and similarity in the NBD and TMD between ABCG2 and selected ABC transporters ABC transporter NBD domain (%)a ABC transporter TM domain (%)b Identity Similarityc Identity Similarity ABCG2 100.0 (234)d 100.0 (234) ABCG2 100.0 (295) 100.0 (295) EcMalK 26.5 (62) 42.7 (100) VcMsbA 9.5 (28) 19.5 (56) TlMalK 22.6 (53) 42.3 (99) EcMsbA 6.4 (19) 18.3 (54) His-P 18.4 (43) 40.6 (95) LcLmrA 8.5 (25) 21.0 (62) MJ1267 17.5 (41) 38.0 (89) Pgp-n 6.1 (18) 19.7 (58) LMR-A 20.9 (49) 40.2 (94) Pgp-c 6.1 (18) 15.6 (46) CFTR-N1 20.5 (48) 34.6 (81) Dro-Wht 22.0 (65) 40.3 (119) TAP1 17.1 (40) 42.7 (100) Pgp-n-reve (16) (30) a Sequence identities and similarities are based on alignments in Fig. 2. b Sequence identities and similarities are based on alignments in Fig. 4. c Similarity is defined for amino acid residues in the alignment, which share common physical or chemical properties such as size, hydrophobicity or charge. Login to comment 123 ABCG2 p.Gln141Lys Patients carrying the Q141K SNP were shown to have elevated drug levels in plasma when treated with topotecan or diflomotecan [22,44-49]. Login to comment 124 ABCG2 p.Gln141Lys From its location in the molecule, the Q141K polymorphism should not disrupt the folding of the subunit; rather it introduces an additional positive charge in an already very positively charged surface (residues R137, R147, K157, R160, and R163 are in close proximity). Login to comment 125 ABCG2 p.Ile239Lys ABCG2 p.Thr237Val Two other NBD mutations, T237V and I239K (OP and SEB, unpublished results), are located near the conserved H-motif in a surface cleft; while the former was fully functional, the latter could not be detected on the cell surface. Login to comment 126 ABCG2 p.Thr237Val In the model, the side chain of T237 is fully exposed to the solvent, a prediction that is consistent with the normal activity of the T237V mutant. Login to comment 127 ABCG2 p.Ile239Lys The side chain of I239, on the other hand, contributes to the hydrophobic core of the protein, and as might be expected from the model, the I239K mutation disrupts the proper folding of the structure and renders the molecule inactive. Login to comment 174 ABCG2 p.Arg309Gly ABCG2 p.Lys86Ile ABCG2 p.Lys86Met ABCG2 p.Gln141Lys ABCG2 p.Val12Met ABCG2 p.Ile239Lys ABCG2 p.Thr237Val Subsequently, a symmetric dimer Y.-F Li et al. / Journal of Molecular Graphics and Modelling 25 (2007) 837-851844 Table 4 Locations of mutations as predicted by the ABCG2 model and functional correlation Mutation Position in ABCG2 Phenotype Reference V12M N-terminal Membrane localization, SNP, and somewhat lower expression and lower resistance [22] S25Pa N-terminal Low drug resistance for the cell line due to lower expression at cell surface [42] T82Aa NBD, Walker A Low drug resistance for the cell line due to lower expression at cell surface [42] K86M NBD, Walker A No expression at cell surface, retained in the Golgi [43] K86I NBD, Walker A No expressed at cell surface [43] Q141K NBD SNP with lower protein expression and low drug resistance [22,23] T237V NBD Fully functional b I239K,R NBD Loss of expression may be due to structural disruption b R309G Linkerc Low drug resistance [42] D315-6 Linker Deletion mutant for A315 and T316. Login to comment 175 ABCG2 p.Gly406Leu ABCG2 p.Gly406Leu ABCG2 p.Gly410Leu ABCG2 p.Gly410Leu It is a splicing variant with a somewhat lower expression and lower resistance [23] A347Ta Linker Low drug resistance [42] G406L, G410L, G406L/G410L GXXXG motif TM1 Dimerization in related proteins. Login to comment 177 ABCG2 p.Arg482Gly ABCG2 p.Gly410Ala ABCG2 p.Gly410Ala ABCG2 p.Gly406Ala ABCG2 p.Gly406Ala ABCG2 p.Glu446Ala Exhibit reduced transport of mitoxantrone, pheophorbide and basal ATPase activity [17] G406A, G410A, G406A/G410A TM1 Fully functional b E446A,D,G,H,K,R,S TM2 Loss of drug resistance [21] R482G,T,M,S, N,D,K,Y TM3 T or G change produces gain of function mutant. Login to comment 179 ABCG2 p.Gly553Leu ABCG2 p.Gly553Glu T mutant binds more tightly to Rhodamin123 and inhibits rhodamine123 transport [19,51,21] G553L, G553E TM5 In drosophila, mutation at this position yields monomer. Login to comment 182 ABCG2 p.Leu554Pro ABCG2 p.Asp620Asn ABCG2 p.Asn557Asp ABCG2 p.His630Glu ABCG2 p.Asn596Gln In sf9 cell, it is expressed on cell surface, but with no ATPase activity [56] L554P TM5 Lowered drug resistance [42] N557D,E TM5 Functional [21] S566Aa ECL (between TM5 and 6) Lowered drug resistance for the cell line [42] N596Q Between TM5 and 6 N-glycosylation site [65] Y605Ca Loop between TM5 and 6 Lowered drug resistance for the cell line [42] D620N Loop between TM5 and 6 SNP polymorphism [22] H630E,L TM6 Functional [21] A632Va TM Lowered drug resistance for the cell line [42] a Mutants not well characterized. Login to comment 204 ABCG2 p.Phe431Ser ABCG2 p.Val556Ser To test these possibilities, we made two mutants, F431S and V556S, and probed cell surface expression with the ABCG2 specific monoclonal antibody 5D3 [39] (Fig. 5A). Login to comment 206 ABCG2 p.Phe431Ser ABCG2 p.Val556Ser Flow cytometry analysis of ABCG2 mutants F431S and V556S. Login to comment 207 ABCG2 p.Phe431Ser ABCG2 p.Val556Ser (A) Using the 5D3 surface antibody, the F431S and V556S mutant proteins are detectable on the cell surface of HEK293 cells. Login to comment 219 ABCG2 p.Val556Ser In particular, the residue V556 in the final model faces G498 in the TM3 helix of the neighboring subunit, explaining the phenotype for the V556S mutant because it faces a small residue. Login to comment 244 ABCG2 p.Gly553Leu ABCG2 p.Gly553Glu Introducing a larger or charged residue at this position (G553L and G553E) would result in a clash of amino acid side chains and disrupt the dimer formation both in ABCG2 and in its Drosophila orthologue. Login to comment 245 ABCG2 p.Arg482Gly It has been hypothesized that residue R482 in TM3 is likely to interact with substrates based on the effect of R482G/T mutations [19]; both are gain-of-function mutants, conferring resistance to a broader range of substrates than the wild-type transporter including rhodamine 123 and doxorubicin [19]. Login to comment