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Vol. 56, Issue 2, 434-447, August 1999
Molecular Neurobiology Branch, Cocaine blocks the normal role of the dopamine transporter (DAT) in
terminating dopamine signaling through molecular interactions that are
only partially understood. Cocaine analog structure-activity studies
have suggested roles for both cationic and aromatic interactions among
DAT, dopamine, and cocaine. We hypothesized that phenylalanine residues lying in putative DAT transmembrane (TM) domains were good
candidates to contribute to aromatic and/or cationic interactions among
DAT, dopamine, and cocaine. To test this idea, we characterized the
influences of alanine substitution for each of 29 phenylalanine residues lying in or near a putative DAT TM domain. Cells express 22 mutants at near wild-type levels, manifest by DAT immunohistochemistry and binding of the radiolabeled cocaine analog
[3H](
)-2-
-carbomethoxy-3-
-(4-fluorophenyl)tropane
(CFT). Seven mutants fail to express at normal levels. Four
mutations selectively reduce cocaine analog affinities. Alanine
substitutions at Phe76, Phe98,
Phe390, and Phe361 located in TM domains 1 and
2, the fourth extracellular loop near TM 4 and in TM 7, displayed
normal affinities for dopamine but 3- to 8-fold reductions in
affinities for CFT. One TM 3 mutation, F155A, selectively
decreased dopamine affinity to less than 3% of wild-type levels while
reducing CFT affinity less than 3-fold. In a current DAT structural
model, each of the residues at which alanine substitution selectively
reduces cocaine analog or dopamine affinities faces a central
transporter cavity, whereas mutations that influence expression levels
are more likely to lie at potential helix/helix interfaces. Specific,
overlapping sets of phenylalanine residues contribute selectively to
DAT recognition of dopamine and cocaine.
Copyright © 1999 by U.S. Government
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