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Do the binding sites of substrates and tricyclic antidepressants overlap on the
human serotonin transporter?
Doctoral thesis at the Medical University of Vienna in partial fulfillment for the degree of
Doctor of Philosophy (PhD)
Univ. Prof. Dr. Michael Freissmuth, MD Professor and Chairman Institute of Pharmacology
Center for Physiology and Pharmacology Medical University of Vienna
Waehringer Strasse 13a A-1090 Vienna, Austria
Vienna, August 2010
With utmost reverence and humility within, I dedicate this sojourn to my Guru, Misha and dearest friend Sonja, who symbolize to me the quintessential epitome of human
Albeit having inherited the oldest living tradition on Earth, with roots reaching
back into prehistory, one of its very few customs I follow blindfolded, without ever
questioning its very rational basis, is that of the ancient Gurukul, wherein ones teacher is
held Supreme in all conceivable realms of conscious existence.
Without the unstinted faith of my Guru, Prof. Michael Freissmuth, I may never
have walked the conglomerate steps I did during the course of this thesis. He inspired me
every moment I breathed during this sojourn. I shall forever be grateful to him for
providing me with the necessary leverage I needed to come out of my shy, inhibited and
reclusive nature and for setting to me a benchmark for self-accomplishment. The doors to
his mind and magnanimous heart were perennially left open to me and he was never
imposing a lesson, to which I will fall back upon for inspiration to leave with posterity
to ponder upon. Perhaps his greatest legacy that I will carry within is the knack of asking
questions - questions perennially reframed to testable hypotheses and amenably
addressed through scientific rigor. He leaves the indelible impression of a great man
With equal sentiment, I am inexplicably indebted for life, to Dr. Sonja Sucic. Her
inimitable selflessness, contagious enthusiasm and honest passion for her life and work
inspired me to emulate her ethic and incorporate in my own. Her steadfast friendship and
contribution to every conceivable aspect of my life crystallized to be the definitive
inspiration towards fruitful execution of my work and in completion of this thesis. The
joy of discovery and experimentation was demonstrated to me by my parents and Guru
but it is what I cherished exploring most, with Dr. Sucic. I, especially am grateful to her
for having refurbished, with a pinch of satire, my very perception towards the ironical
vagaries of life. She commands the most profound influence on my philosophical
underpinnings in the way I approach life today.
Besides, I am grateful to Prof. Harald H. Sitte and his group who helped expand
my work to include a more holistic understanding of monoamine transporter inhibition. I
also express my gratitude to Prof. Gerhard F. Ecker and his graduate student Mag. Ren
Weissensteiner, for their insights from computational biology enabled me to generate
hypotheses towards designing experiments in an iterative approach. I wish to congratulate
all my colleagues in the laboratory for providing me with a productive atmosphere
necessary to work in an efficient manner. Especially, Mr. Ali El-Kasaby with whom I
enjoyed my humble origins in the laboratory and developed a formidable friendship to
last for a lifetime. I am thankful to Mrs. Ludmilla Hertting and late Mrs. Alice Zafaurek
for their kind support with administrative affairs and extend my gratitudes to Prof.
Werner Sieghart (Medical University of Vienna, Austria), Prof. Stefan Bhm (Medical
University of Vienna, Austria), Prof. Nicholas Singewald (Medical University of
Innsbruck, Austria), Prof. Cord-Michael Becker (University of Erlangen-Nrnberg,
Germany) and Prof. Menahem Segal (The Weizmann Institute of Science, Rehovot,
Israel), for their critique and encouragement served to maintain direction during my
In addition, I humbly acknowledge the financial support received for my research
from the Austrian Science Fund (FWF) and the Medical University of Vienna in the Cell
Communication in Health and Disease (CCHD) Doctoral Program.
Finally, my endearing set of parents, is the very reason I ever had the opportunity
to walk in pursuit of my childhood fascination to discover the world I inherited in a
dedicated endeavor. Their steadfast friendship, love, affection, belief and towering
inspiration helped me to withstand rigors in between. I am grateful to life for letting me
know my parents closely!
August 6, 2010
Sarker, S., Weissensteiner, R., Steiner, I., Sitte, HH., Ecker, GF., Freissmuth, M., Sucic,
S. (2010) The high-affinity binding site for tricyclic antidepressants resides in the outer
vestibule of the serotonin transporter (in revision).
Sarker, S., Steiner, I. (2008) Do the binding sites of substrates and tricyclic
antidepressants overlap on the human serotonin transporter? BMC Pharmacol.8
(Suppl.):A9. 14th Scientific Symposium of the Austrian Pharmacological Society
(APHAR), Innsbruck, Austria, 21-22 November, 2008.
To: Michael Freissmuth
ReplyTo: Richard Kim , firstname.lastname@example.org
Subject: MOLPHARM/2010/067538-Revision Invitation
Cc: Richard Kim
Dear Dr. Freissmuth:
Your manuscript entitled "THE HIGH-AFFINITY BINDING SITE FOR TRICYCLIC
ANTIDEPRESSANTS RESIDES IN THE OUTER VESTIBULE OF THE SEROTONIN
TRANSPORTER" has been reviewed by two experts familiar with this field. Please visit
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checklist. We would be willing to consider a revised manuscript; however, it will have to
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Reviewer 1 Comments for the Author...
This manuscript presents the results of an investigation into the interaction of tricyclic
antidepressants (TCAs) with the serotonin transporter (SERT). Crystallographic analysis
of the bacterial LeuT homolog identified specific binding sites for TCAs, and some
authors have postulated that the same regions and types of interactions apply to SERTs.
However, while TCAs are competitive inhibitors of SERTs, they are low-affinity,
noncompetitive inhibitors of LeuT, suggesting a different type and site of interaction. In
this work Sarker et al combine molecular modeling with functional measurements
(including mutagenesis) to provide a working model for the TCA binding site of SERT.
The work is carefully done, and the results support the conclusions. However, there are
several aspects of the work that need expansion, as detailed below.
p. 7: We also verified that the model was consistent with the results from previous
mutagenesis studies.. Please elaborate on what the criteria were and how th