pH-Dependent Structural Change in Neoculin with Special Reference to Its Taste-Modifying Activity

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

doi:10.1271/bbb.90524

“…1 and 2B). Although the pattern of this spectrum change differed from that of the pH-dependent spectrum (pH 7.0-3.0), as explained in a previous paper, 12) we found here that undissociated weak acids can induce a conformational change in neoculin causing its intense sweetness.…”

supporting

confidence: 45%

“…The far-UV CD spectrum of neoculin was uniform over a range of pH 2.0-10.0, but its intrinsic tryptophan (Trp) fluorescence changed with decreases in pH, probably due to a conformational change of neoculin from inactive to active form. 12) Then we performed an intrinsic Trp fluorescence spectroscopic analysis to determine whether the structure of neoculin changes in solutions of sodium acetate buffer of different concentrations at the same pH. The spectrum of neoculin varied with increases in the concentration of sodium acetate buffer from 0.01 mM to 1,000 mM at pH 5.0.…”

mentioning

confidence: 99%

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

Nakajima

¹

,

Koizumi

²

,

Iizuka

³

et al. 2011

Bioscience, Biotechnology, and Biochemistry

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“…Several essential amino acids that are responsible for the taste-modifying properties of neoculin have been identi ed: His-11 in NBS is responsible for the pH-dependent taste-modifying activity of neoculin [25], and Arg-48, Tyr-65, Val-72, and Phe-94 function in the binding and activation of human sweet taste receptors [26]. Changes in the tertiary structure of the subunits at these residues are thought to contribute to the taste-modifying properties of neoculin [27,28].…”

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

Okubo

¹

,

Terauchi

²

,

Okada

³

et al. 2021

Preprint

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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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“…Several essential amino acids that are responsible for the taste-modifying properties of neoculin have been identified: His-11 in NBS is responsible for the pH-dependent taste-modifying activity of neoculin [ 25 ], and Arg-48, Tyr-65, Val-72, and Phe-94 function in the binding and activation of human sweet taste receptors [ 26 ]. Changes in the tertiary structure of the subunits at these residues are thought to contribute to the taste-modifying properties of neoculin [ 27 , 28 ].…”

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

Okubo

¹

,

Terauchi

²

,

Okada

³

et al. 2021

BMC Genomics

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1

0

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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.

show abstract

pH-Dependent Structural Change in Neoculin with Special Reference to Its Taste-Modifying Activity

Cited by 6 publications

References 13 publications

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

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

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

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