Evidence for distinct sodium-, dopamine-, and cocaine-dependent conformational changes in transmembrane segments 7 and 8 of the dopamine transporter
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Evidence for distinct sodium-, dopamine-, and cocaine-dependent conformational changes in transmembrane segments 7 and 8 of the dopamine transporter. / Norregaard, Lene; Loland, Claus Juul; Gether, Ulrik.
In: The Journal of Biological Chemistry, Vol. 278, No. 33, 15.08.2003, p. 30587-96.Research output: Contribution to journal › Journal article › Research › peer-review
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TY - JOUR
T1 - Evidence for distinct sodium-, dopamine-, and cocaine-dependent conformational changes in transmembrane segments 7 and 8 of the dopamine transporter
AU - Norregaard, Lene
AU - Loland, Claus Juul
AU - Gether, Ulrik
PY - 2003/8/15
Y1 - 2003/8/15
N2 - Previously we obtained evidence based on engineering of Zn2+ binding sites that the extracellular parts of transmembrane segment 7 (TM7) and TM8 in the human dopamine transporter are important for transporter function. To further evaluate the role of this domain, we have employed the substituted cysteine accessibility method and performed 10 single cysteine substitutions at the extracellular ends of TM7 and TM8. The mutants were made in background mutants of the human dopamine transporter with either two (E2C) or five endogenous cysteines substituted (X5C) that render the transporter largely insensitive to cysteine modification. In two mutants (M371C and A399C), treatment with the sulfhydryl-reactive reagent [2-(trimethylammonium)-ethyl]methanethiosulfonate (MTSET) led to a substantial inhibition of [3H]dopamine uptake. In M371C this inactivation was enhanced by Na+ and blocked by dopamine. Inhibitors such as cocaine did not alter the effect of MTSET in M371C. The protection of M371C inactivation by dopamine required Na+. Because dopamine binding is believed to be Na+-independent, this suggests that dopamine induces a transport-associated conformational change that decreases the reactivity of M371C with MTSET. In contrast to M371C, cocaine decreased the reaction rate of A399C with MTSET, whereas dopamine had no effect. The protection by cocaine can either reflect that Ala-399 lines the cocaine binding crevice or that cocaine induces a conformational change that decreases the reactivity of A399C. The present findings add new functionality to the TM7/8 region by providing evidence for the occurrence of distinct Na+-, substrate-, and perhaps inhibitor-induced conformational changes critical for the proper function of the transporter.
AB - Previously we obtained evidence based on engineering of Zn2+ binding sites that the extracellular parts of transmembrane segment 7 (TM7) and TM8 in the human dopamine transporter are important for transporter function. To further evaluate the role of this domain, we have employed the substituted cysteine accessibility method and performed 10 single cysteine substitutions at the extracellular ends of TM7 and TM8. The mutants were made in background mutants of the human dopamine transporter with either two (E2C) or five endogenous cysteines substituted (X5C) that render the transporter largely insensitive to cysteine modification. In two mutants (M371C and A399C), treatment with the sulfhydryl-reactive reagent [2-(trimethylammonium)-ethyl]methanethiosulfonate (MTSET) led to a substantial inhibition of [3H]dopamine uptake. In M371C this inactivation was enhanced by Na+ and blocked by dopamine. Inhibitors such as cocaine did not alter the effect of MTSET in M371C. The protection of M371C inactivation by dopamine required Na+. Because dopamine binding is believed to be Na+-independent, this suggests that dopamine induces a transport-associated conformational change that decreases the reactivity of M371C with MTSET. In contrast to M371C, cocaine decreased the reaction rate of A399C with MTSET, whereas dopamine had no effect. The protection by cocaine can either reflect that Ala-399 lines the cocaine binding crevice or that cocaine induces a conformational change that decreases the reactivity of A399C. The present findings add new functionality to the TM7/8 region by providing evidence for the occurrence of distinct Na+-, substrate-, and perhaps inhibitor-induced conformational changes critical for the proper function of the transporter.
KW - Amino Acid Sequence
KW - Animals
KW - COS Cells
KW - Cocaine
KW - Dopamine
KW - Dopamine Plasma Membrane Transport Proteins
KW - Dopamine Uptake Inhibitors
KW - Extracellular Space
KW - Humans
KW - Indicators and Reagents
KW - Membrane Glycoproteins
KW - Membrane Transport Proteins
KW - Mesylates
KW - Molecular Sequence Data
KW - Mutagenesis, Site-Directed
KW - Nerve Tissue Proteins
KW - Protein Conformation
KW - Protein Structure, Tertiary
KW - Radioligand Assay
KW - Sodium
KW - Tritium
KW - Zinc
U2 - 10.1074/jbc.M303854200
DO - 10.1074/jbc.M303854200
M3 - Journal article
C2 - 12773538
VL - 278
SP - 30587
EP - 30596
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
SN - 0021-9258
IS - 33
ER -
ID: 47293825