Abstracts - Association for Chemoreception Sciences

#P197 POSTER SESSION IV: CHEMOSENSORY
TRANSDUCTION AND SIGNALING
Residual Glucose Taste in T1R3 Knockout but not TRPM5
Knockout Mice
Steven Zukerman 1 , Robert F. Margolskee 2 , Anthony Sclafani 1
1
Brooklyn College of CUNY Brooklyn, NY, USA, 2 Monell
Chemical Senses Center Philadelphia, PA, USA
Deletion of the genes for the sweet taste receptor subunit T1R3 or
the taste signaling protein TRPM5 greatly attenuates sweetener
preference in mice. However, knockout (KO) mice missing T1R3
or TRPM5 develop preferences for glucose but not fructose in 24-
h tests which is attributed to the post-oral reinforcing actions of
glucose. The present study probed for residual glucose taste
sensitivity in KO mice. Water deprived T1R3 KO, TRPM5 KO
and C57BL/6 (B6) control mice displayed similar lick rates for
8% glucose and 8% fructose in 1-min, 2-bottle choice tests.
However, when food deprived the KO mice licked very little for
either sugar while B6 mice continued to lick for both sugars in 1-
min tests. Yet, when the test was extended to 1 h, T1R3 KO mice
now displayed a significant glucose preference (66%) while the B6
mice initially preferred fructose (59%). In 1-h, 1-bottle tests,
T1R3 KO and B6 mice licked more for glucose than fructose and
both groups preferred glucose in a subsequent 1-h, 2-bottle test.
However, the glucose preference was greater in T1R3 KO than B6
mice (86 vs. 67%). The TRPM5 KO mice remained indifferent
and licked very little for either sugar in these 1-h tests. In 24-h
tests, however, the TRPM5 KO mice licked much more for
glucose than fructose. The 1-h data suggest a residual glucose taste
sensitivity in T1R3 KO mice which may be mediated by their
intact T1R2 sweet receptor or a glucose polymer (polycose) taste
receptor. TRPM5 KO mice lack this residual glucose taste but
learn to prefer glucose to fructose in 24-h tests based on post-oral
glucose reinforcement. Post-oral reinforcement can also explain
the preference B6 mice develop for glucose over fructose.
Acknowledgements: NIH grants DK031135 (AS), DC03055 and
DC03155 (RFM)
#P198 POSTER SESSION IV: CHEMOSENSORY
TRANSDUCTION AND SIGNALING
Herbicides and Antilipid Drugs Block Human T1R3 Receptors
Bedrich Mosinger 1 , Zaza Kokrashvili 1 , Robert F Margolskee 1 ,
Emeline L Maillet 2
1
Monell Chemical Senses Center Philadelphia, PA, USA,
2
Mount Sinai School of Medicine New York, NY, USA
We have found that ubiquitous phenoxy-auxin herbicides and
lipid-lowering fibrate drugs are potent inhibitors of the human
T1R3 receptor, but not of the rodent form. T1R3 is expressed in
taste cells, endocrine pancreas and enteroendocrine cells of the
gastrointestinal tract. In the taste system it forms distinct
receptors for sweet compounds and amino-acids. In the intestine
and endocrine system it is functionally engaged in the regulation
of glucose metabolism and hormone release. Fibrates and
phenoxy-herbicides inhibit human T1R3 with a potency
comparable to that shown by fibrates acting on their known
target, the peroxisome proliferator-activated receptor alpha
(PPARalpha). T1R3 thus may be a primary target of fibrates,
underlying certain of their beneficial effects in treating
hyperlipidemia and type II diabetes. Likewise, phenoxyherbicides’
effects on T1R3 may underlie certain of their side
effects in humans that due to the species differences in T1R3
would have gone undetected in studies on rodents. This study
was supported in part by NIH grants DC007984 to E.L.M.,
DC008301 to R.F.M, and DC007399 and DK073248 to B.M.
#P199 POSTER SESSION IV: CHEMOSENSORY
TRANSDUCTION AND SIGNALING
Allosteric regulation of taste chemosensors: insights from
molecular modeling and docking
Wely B. Floriano 1,2 , Desiree Daniels 3 , Chloe Thai 3
1
Lakehead University and the Biorefining Research Initiative
Thunder Bay, ON, Canada, 2 Thunder Bay Regional Research
Institute Thunder Bay, ON, Canada, 3 California State Polytechnic
University Pomona Pomona, CA, USA
Modulation of GPCR activity by a ligand binding to an allosteric
site, which is topographically distinct from the active site, is a
well-studied mechanism in the context of pharmacologicallyrelevant
GPCRs. An allosteric modulator can enhance or reduce
receptor response to its endogenous agonist, without changing
receptor-agonist interaction directly. In the context of taste
response, allosteric regulation has tremendous potential. Natural
sugars could be enhanced to provide more sweetness without the
need to increase the amount of sugar. The flavor of protein-rich
foods could be enhanced without the need to resort to unhealthy
strategies such as increasing salt content. Here we present a
molecular-level view of allosteric regulation for class C GPCR
chemosensors. Comparative modeling and molecular docking
were used to investigate potential regulatory sites for atomic ions,
amino acids and nucleosides in these receptors. We discuss the
physicochemical nature of these sites and suggest scaffolds for
potential modulators of human sweet and umami taste response.
#P200 POSTER SESSION IV: CHEMOSENSORY
TRANSDUCTION AND SIGNALING
Direct NMR measurement of ligand binding to the human
sweet taste receptor domains
Rani Parvathy 1 , Outhiriaradjou Benard 2 , Mike Goran 1 ,
John L. Markley 1,3 , Marianna Max 2 , Fariba Assadi-Porter 1,3
1
University of Wisconsin-Madison, NMRFAM Madison, WI, USA,
2
Mt. Sinai School of Medicine New York, NY, USA, 3 NMR Facility
at Madison Madison, WI, USA
The human sweet taste receptor is a class C G-protein coupled
receptor (GPCR). The receptor exists as a heterodimer and
composed of two subunits, T1R2 and T1R3. Each subunit
contains three subdomains: amino terminal domain (ATD),
cycteine rich domain (CRD) and transmembrane domain (TMD).
We have studied the binding properties of small molecule
sweeteners and the sweet tasting protein, brazzein to subdomains
of the sweet receptor. For this purpose we have cloned and
purified different domains of the receptor protein. For the T1R2
subunit, we constructed the ATD whereas for the T1R3 subunit
we made three constructs, ATD+CRD, TMD and the full-length
subunit. The proteins were expressed by bacterial expression and
by cell-free translation systems. We used Saturation Transfer
Difference (STD) NMR to monitor direct binding of a panel of
small molecule sweeteners, neotame, lactisole, cyclamate,
dextrose, alitame and sucralose to the receptor sub-domains.
We monitored brazzein binding to the receptor extracellular
domains by two-dimensional 1 H- 15 N HQSC NMR. Brazzein
showed binding to both ATD-T1R2 and ATD+CDR-T1R3 while
P O S T E R S
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