Non-Acidic Compounds Induce the Intense Sweet Taste of Neoculin, a Taste-Modifying Protein

Nakajima, Ken-ichiro; Koizumi, Ayako; Iizuka, Kazuaki; Ito, Keisuke; Morita, Yuji; Koizumi, Taichi; Asakura, Tomiko; Shimizu‐Ibuka, Akiko; Misaka, Takumi; Abe, Keiko

doi:10.1271/bbb.110081

Cited by 5 publications

(2 citation statements)

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“…Nakajima et al . reported that neoculin has a strong sweet taste at pH 6.3 in the presence of 100 mM ammonium chloride or at pH 8.0 in the presence of 100 mM ammonium acetate [ 13 ]. The effect of the ammonium ion would be similar to that of the role of the protonated Lys90 residue, which interrupts the His11-Asp91 interaction to make the mutant sweet at neutral pH.…”

Section: Discussionmentioning

confidence: 99%

Structural Basis of pH Dependence of Neoculin, a Sweet Taste-Modifying Protein

et al. 2015

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Among proteins utilized as sweeteners, neoculin and miraculin are taste-modifying proteins that exhibit pH-dependent sweetness. Several experiments on neoculin have shown that His11 of neoculin is responsible for pH dependence. We investigated the molecular mechanism of the pH dependence of neoculin by molecular dynamics (MD) calculations. The MD calculations for the dimeric structures of neoculin and His11 mutants showed no significant structural changes for each monomer at neutral and acidic pH levels. The dimeric structure of neoculin dissociated to form isolated monomers under acidic conditions but was maintained at neutral pH. The dimeric structure of the His11Ala mutant, which is sweet at both neutral and acidic pH, showed dissociation at both pH 3 and 7. The His11 residue is located at the interface of the dimer in close proximity to the Asp91 residue of the other monomer. The MD calculations for His11Phe and His11Tyr mutants demonstrated the stability of the dimeric structures at neutral pH and the dissociation of the dimers to isolated monomers. The dissociation of the dimer caused a flexible backbone at the surface that was different from the dimeric interface at the point where the other monomer interacts to form an oligomeric structure. Further MD calculations on the tetrameric structure of neoculin suggested that the flexible backbone contributed to further dissociation of other monomers under acidic conditions. These results suggest that His11 plays a role in the formation of oligomeric structures at pH 7 and that the isolated monomer of neoculin at acidic pH is responsible for sweetness.

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Section: Discussionmentioning

confidence: 99%

Structural Basis of pH Dependence of Neoculin, a Sweet Taste-Modifying Protein

et al. 2015

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“…Furthermore, neoculin has a taste-modifying activity that converts sourness to sweetness: for example, the sour taste of lemons is changed to a sweet orange taste. Moreover, the presence of neoculin induces sweetness in drinking water, and some organic acids taste sweet when consumed after neoculin [ 21 ]. Neoculin is perceived by the human sweet taste receptor T1R2-T1R3, a member of the G-protein-coupled receptor family [ 22 ].…”

Section: Introductionmentioning

confidence: 99%

De novo transcriptome analysis and comparative expression profiling of genes associated with the taste-modifying protein neoculin in Curculigo latifolia and Curculigo capitulata fruits

et al. 2021

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Background Curculigo latifolia is a perennial plant endogenous to Southeast Asia whose fruits contain the taste-modifying protein neoculin, which binds to sweet receptors and makes sour fruits taste sweet. Although similar to snowdrop (Galanthus nivalis) agglutinin (GNA), which contains mannose-binding sites in its sequence and 3D structure, neoculin lacks such sites and has no lectin activity. Whether the fruits of C. latifolia and other Curculigo plants contain neoculin and/or GNA family members was unclear. Results Through de novo RNA-seq assembly of the fruits of C. latifolia and the related C. capitulata and detailed analysis of the expression patterns of neoculin and neoculin-like genes in both species, we assembled 85,697 transcripts from C. latifolia and 76,775 from C. capitulata using Trinity and annotated them using public databases. We identified 70,371 unigenes in C. latifolia and 63,704 in C. capitulata. In total, 38.6% of unigenes from C. latifolia and 42.6% from C. capitulata shared high similarity between the two species. We identified ten neoculin-related transcripts in C. latifolia and 15 in C. capitulata, encoding both the basic and acidic subunits of neoculin in both plants. We aligned these 25 transcripts and generated a phylogenetic tree. Many orthologs in the two species shared high similarity, despite the low number of common genes, suggesting that these genes likely existed before the two species diverged. The relative expression levels of these genes differed considerably between the two species: the transcripts per million (TPM) values of neoculin genes were 60 times higher in C. latifolia than in C. capitulata, whereas those of GNA family members were 15,000 times lower in C. latifolia than in C. capitulata. Conclusions The genetic diversity of neoculin-related genes strongly suggests that neoculin genes underwent duplication during evolution. The marked differences in their expression profiles between C. latifolia and C. capitulata may be due to mutations in regions involved in transcriptional regulation. Comprehensive analysis of the genes expressed in the fruits of these two Curculigo species helped elucidate the origin of neoculin at the molecular level.

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Non‐Catalytic Industrial Proteins

Walsh

2015

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Non-Acidic Compounds Induce the Intense Sweet Taste of Neoculin, a Taste-Modifying Protein

Cited by 5 publications

References 14 publications

Structural Basis of pH Dependence of Neoculin, a Sweet Taste-Modifying Protein

Structural Basis of pH Dependence of Neoculin, a Sweet Taste-Modifying Protein

De novo transcriptome analysis and comparative expression profiling of genes associated with the taste-modifying protein neoculin in Curculigo latifolia and Curculigo capitulata fruits

Non‐Catalytic Industrial Proteins

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