ABCMdb

PMID: 10375401

Zhou Y, Gottesman MM, Pastan I
The extracellular loop between TM5 and TM6 of P-glycoprotein is required for reactivity with monoclonal antibody UIC2.
Arch Biochem Biophys. 1999 Jul 1;367(1):74-80., [PubMed]

Sentences

No. Mutations Sentence Comment

66 ABCB1 p.Gly324Lys ABCB1 p.Leu322Ile ABCB1 p.Gln330Asn ABCB1 p.Leu332Met ABCB1 p.Val331Ala ABCB1 p.Ser327Thr ABCB1 p.Thr318Ser Those substitutions are T318S, L322I, G324K, S327T, Q330N, V331A, and L332M (Fig. 1). Login to comment 78 ABCB1 p.Gln330Asn ABCB1 p.Leu332Met ABCB1 p.Val331Ala This possibility was examined by testing the UIC2 reactivity of a P-gp mutant, MDR1/ MDR2(330-332), which carried substitutions Q330N, V331A, and L332M in TM6. Login to comment 79 ABCB1 p.Gln330Asn ABCB1 p.Leu332Met ABCB1 p.Val331Ala This possibility was examined by testing the UIC2 reactivity of a P-gp mutant, MDR1/ MDR2(330-332), which carried substitutions Q330N, V331A, and L332M in TM6. Login to comment 83 ABCB1 p.Gln330Asn ABCB1 p.Leu332Met ABCB1 p.Val331Ala However, in the presence of cyclosporin A, cells expressing MDR1/MDR2(330-332) displayed a number of UIC2 binding sites more similar to cells expressing wild-type P-gp, indicating that the triple mutation (Q330N, V331A, and L332M) in TM6 did not directly affect the affinity of UIC2 for its epitope (Fig. 4). Login to comment 84 ABCB1 p.Gln330Asn ABCB1 p.Leu332Met ABCB1 p.Val331Ala However, in the presence of cyclosporin A, cells expressing MDR1/MDR2(330-332) displayed a number of UIC2 binding sites more similar to cells expressing wild-type P-gp, indicating that the triple mutation (Q330N, V331A, and L332M) in TM6 did not directly affect the affinity of UIC2 for its epitope (Fig. 4). Login to comment 106 ABCB1 p.Gly324Lys ABCB1 p.Leu322Ile ABCB1 p.Ser327Thr ABCB1 p.Thr318Ser DISCUSSION The Extracellular Loop between TM5 and TM6 Is Essential for UIC2 Recognition In this work, we found that a quadruple substitution of MDR2 residues (T318S, L322I, G324K, and S327T) in the extracellular loop between TM5 and TM6 abolished UIC2 recognition of P-gp. Login to comment 107 ABCB1 p.Gly324Lys ABCB1 p.Leu322Ile ABCB1 p.Ser327Thr ABCB1 p.Thr318Ser DISCUSSION The Extracellular Loop between TM5 and TM6 Is Essential for UIC2 Recognition In this work, we found that a quadruple substitution of MDR2 residues (T318S, L322I, G324K, and S327T) in the extracellular loop between TM5 and TM6 abolished UIC2 recognition of P-gp. Login to comment 114 ABCB1 p.Gly324Lys ABCB1 p.Leu322Ile ABCB1 p.Ser327Thr ABCB1 p.Thr318Ser Since the substitutions T318S, L322I, G324K, and S327T had little effect on either MRK-16 labeling or multidrug transporter activity, it is less likely that these mutations produce any major changes in P-gp structure. Login to comment 115 ABCB1 p.Gly324Lys ABCB1 p.Leu322Ile ABCB1 p.Gln330Asn ABCB1 p.Leu332Met ABCB1 p.Val331Ala ABCB1 p.Ser327Thr ABCB1 p.Thr318Ser Since the substitutions T318S, L322I, G324K, and S327T had little effect on either MRK-16 labeling or multidrug transporter activity, it is less likely that these mutations produce any major changes in P-gp structure. Login to comment 116 ABCB1 p.Gln330Asn ABCB1 p.Leu332Met ABCB1 p.Val331Ala UIC2 Reactivity Is Sensitive to Mutations in TM6 A triple mutation, Q330N, V331A, and L332M, in TM6 decreased overall multidrug transporter activity FIG. 3. FACS analysis of cell surface expression of MDR1 and MDR1/MDR2(330-332) using MRK-16 and UIC2. Login to comment