Abstract:
Stevia rebaudiana Bertoni is one of the sweeteners with the highest customer demand due
to its natural origin and low-calorie content. The primary bioactive substances in Stevia
rebaudiana leaves are steviol glycosides which are responsible for the sweetness. But a
bitter-off flavor of steviol glycosides is the main barrier to its commercialization as a
natural sweetener. The human bitter taste receptors hTAS2R4 and hTAS2R14 are
selectively activated by steviol glycosides according to recent in vitro experiments in HEK
293 cells. Aim of the study was to investigate the molecular interactions that cause the
bitter aftertaste of steviol glycosides and suggest inhibition prediction using a
computational approach. To achieve this, structural modelling of hTAS2R4 and
hTAS2R14 was performed, followed by molecular docking of TAS2R4, 14 models with
steviol glycosides and their recognized competitive inhibitors. Comparison of scoring
range was done that how inhibitors and steviol glycosides interact with bitter taste receptors
at the molecular level. Results showed that bitteness is caused by amino acids' capacity to
form hydrogen bonds with other amino acids in binding pocket found at the extracellular
termini of TAS2R4 and TAS2R14.The results demonstrated that steviol glycosides have
only a single site for orthosteric binding to these receptors. Strong binding interactions
exist between Rebaudioside B, C, D, E, and F and TAS2R4, TAS2R14. Steviolbioside was
the least interacting with both receptors, while Dulcoside A, Rubusoside, and Rebaudioside
A exhibited weaker interactions. TAS2R4 revealed strong molecular interactions with its
discovered competitive inhibitors based on their IC50 values. The BCML inhibitor, which
is the most efficient, has an IC50 value of 59 nM. On the other hand, the least active IC50
values for TAS2R14 suggested weaker molecular interactions, which would explain these
weak interactions. As an outcome, the proposed binding interactions of steviol glycosides
and competitive inhibitors, development of methods to diminish unwanted characteristics,
like bitterness, from this type of sweetener may be achievable with the aid of the hT2R4
and hT2R14 taste receptors structural model that were modeled in this study.
