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Thomas Hofmann - One of the best experts on this subject based on the ideXlab platform.
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Structures, Sensory Activity, and Dose/Response Functions of 2,5-Diketopiperazines in Roasted Cocoa Nibs (Theobroma cacao)
Journal of Agricultural and Food Chemistry, 2005Co-Authors: Timo D. Stark, Thomas HofmannAbstract:The taste compounds inducing the blood-like, metallic bitter taste sensation reported recently for a dichloromethane extract prepared from roasted cocoa nibs were identified as a series of 25 diketopiperazines by means of HPLC degustation, LC−MS/MS, and independent synthesis. Among these 25 compounds, 13 cis-configured diketopiperazines, namely, cyclo(l-IIe-l-Phe), cyclo(l-Val-l-Leu), cyclo(l-Pro-l-Pro), cyclo(l-IIe-l-Pro), cyclo(l-Val-l-Tyr), cyclo(l-Ala-l-Tyr), cyclo(l-Phe-l-Ser), cyclo(l-Ala-l-IIe), cyclo(l-Leu-l-Phe), cyclo(l-Pro-l-Val), cyclo(l-Pro-l-Thr), cyclo(l-Pro-l-Tyr), and cyclo(l-Val-l-Val) were identified for the first time in cocoa. In addition, the taste recognition thresholds for the metallic as well as the bitter taste of the diketopiperazines were determined, and after quantitative analysis by using two diastereomeric diketopiperazines as the internal standards, the sensory impact of the diketopiperazines was evaluated on the basis of their dose-over-threshold (DoT) factors calculated a...
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structures sensory activity and dose response functions of 2 5 diketopiperazines in roasted cocoa nibs theobroma cacao
Journal of Agricultural and Food Chemistry, 2005Co-Authors: Timo D. Stark, Thomas HofmannAbstract:The taste compounds inducing the blood-like, metallic bitter taste sensation reported recently for a dichloromethane extract prepared from roasted cocoa nibs were identified as a series of 25 diketopiperazines by means of HPLC degustation, LC−MS/MS, and independent synthesis. Among these 25 compounds, 13 cis-configured diketopiperazines, namely, cyclo(l-IIe-l-Phe), cyclo(l-Val-l-Leu), cyclo(l-Pro-l-Pro), cyclo(l-IIe-l-Pro), cyclo(l-Val-l-Tyr), cyclo(l-Ala-l-Tyr), cyclo(l-Phe-l-Ser), cyclo(l-Ala-l-IIe), cyclo(l-Leu-l-Phe), cyclo(l-Pro-l-Val), cyclo(l-Pro-l-Thr), cyclo(l-Pro-l-Tyr), and cyclo(l-Val-l-Val) were identified for the first time in cocoa. In addition, the taste recognition thresholds for the metallic as well as the bitter taste of the diketopiperazines were determined, and after quantitative analysis by using two diastereomeric diketopiperazines as the internal standards, the sensory impact of the diketopiperazines was evaluated on the basis of their dose-over-threshold (DoT) factors calculated a...
Ashwini Nangia - One of the best experts on this subject based on the ideXlab platform.
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Water mediated tube in tetrapeptide cyclo(Phe-Pro-Leu-Aha) trihydrate and crystal structure of cyclo(D-Phe-Pro-Leu-Aha) anhydrate
CrystEngComm, 2007Co-Authors: B. M. Rajesh, Javed Iqbal, N. Jagadeesh Babu, Ashwini NangiaAbstract:Water molecules connect 6.5 × 4.5 A diameter rings in the X-ray crystal structure of 16-member tetrapeptide cyclo(Phe-Pro-Leu-Aha) (1) trihydrate. However, stereoisomer cyclo(D-Phe-Pro-Leu-Aha) (2) crystallized in anhydrate form. Structural differences in L- to D-amino acid exchanged cyclic peptides are analyzed.
Timo D. Stark - One of the best experts on this subject based on the ideXlab platform.
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Structures, Sensory Activity, and Dose/Response Functions of 2,5-Diketopiperazines in Roasted Cocoa Nibs (Theobroma cacao)
Journal of Agricultural and Food Chemistry, 2005Co-Authors: Timo D. Stark, Thomas HofmannAbstract:The taste compounds inducing the blood-like, metallic bitter taste sensation reported recently for a dichloromethane extract prepared from roasted cocoa nibs were identified as a series of 25 diketopiperazines by means of HPLC degustation, LC−MS/MS, and independent synthesis. Among these 25 compounds, 13 cis-configured diketopiperazines, namely, cyclo(l-IIe-l-Phe), cyclo(l-Val-l-Leu), cyclo(l-Pro-l-Pro), cyclo(l-IIe-l-Pro), cyclo(l-Val-l-Tyr), cyclo(l-Ala-l-Tyr), cyclo(l-Phe-l-Ser), cyclo(l-Ala-l-IIe), cyclo(l-Leu-l-Phe), cyclo(l-Pro-l-Val), cyclo(l-Pro-l-Thr), cyclo(l-Pro-l-Tyr), and cyclo(l-Val-l-Val) were identified for the first time in cocoa. In addition, the taste recognition thresholds for the metallic as well as the bitter taste of the diketopiperazines were determined, and after quantitative analysis by using two diastereomeric diketopiperazines as the internal standards, the sensory impact of the diketopiperazines was evaluated on the basis of their dose-over-threshold (DoT) factors calculated a...
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structures sensory activity and dose response functions of 2 5 diketopiperazines in roasted cocoa nibs theobroma cacao
Journal of Agricultural and Food Chemistry, 2005Co-Authors: Timo D. Stark, Thomas HofmannAbstract:The taste compounds inducing the blood-like, metallic bitter taste sensation reported recently for a dichloromethane extract prepared from roasted cocoa nibs were identified as a series of 25 diketopiperazines by means of HPLC degustation, LC−MS/MS, and independent synthesis. Among these 25 compounds, 13 cis-configured diketopiperazines, namely, cyclo(l-IIe-l-Phe), cyclo(l-Val-l-Leu), cyclo(l-Pro-l-Pro), cyclo(l-IIe-l-Pro), cyclo(l-Val-l-Tyr), cyclo(l-Ala-l-Tyr), cyclo(l-Phe-l-Ser), cyclo(l-Ala-l-IIe), cyclo(l-Leu-l-Phe), cyclo(l-Pro-l-Val), cyclo(l-Pro-l-Thr), cyclo(l-Pro-l-Tyr), and cyclo(l-Val-l-Val) were identified for the first time in cocoa. In addition, the taste recognition thresholds for the metallic as well as the bitter taste of the diketopiperazines were determined, and after quantitative analysis by using two diastereomeric diketopiperazines as the internal standards, the sensory impact of the diketopiperazines was evaluated on the basis of their dose-over-threshold (DoT) factors calculated a...
James E. Bina - One of the best experts on this subject based on the ideXlab platform.
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Vibrio cholerae ToxR Downregulates Virulence Factor Production in Response to Cyclo(Phe-Pro)
mBio, 2013Co-Authors: X. Renee Bina, Dawn L. Taylor, Amit Vikram, Vanessa M. Ante, James E. BinaAbstract:Vibrio cholerae is an aquatic organism that causes the severe acute diarrheal disease cholera. The ability of V. cholerae to cause disease is dependent upon the production of two critical virulence determinants, cholera toxin (CT) and the toxin-coregulated pilus (TCP). The expression of the genes that encode for CT and TCP production is under the control of a hierarchical regulatory system called the ToxR regulon, which functions to activate virulence gene expression in response to in vivo stimuli. Cyclic dipeptides have been found to be produced by numerous bacteria, yet their biological function remains unknown. V. cholerae has been shown to produce cyclo(Phe-Pro). Previous studies in our laboratory demonstrated that cyclo(Phe-Pro) inhibited V. cholerae virulence factor production. For this study, we report on the mechanism by which cyclo(Phe-Pro) inhibited virulence factor production. We have demonstrated that exogenous cyclo(Phe-Pro) activated the expression of leuO, a LysR-family regulator that had not been previously associated with V. cholerae virulence. Increased leuO expression repressed aphA transcription, which resulted in downregulation of the ToxR regulon and attenuated CT and TCP production. The cyclo(Phe-Pro)-dependent induction of leuO expression was found to be dependent upon the virulence regulator ToxR. Cyclo(Phe-Pro) did not affect toxR transcription or ToxR protein levels but appeared to enhance the ToxR-dependent transcription of leuO. These results have identified leuO as a new component of the ToxR regulon and demonstrate for the first time that ToxR is capable of downregulating virulence gene expression in response to an environmental cue. Importance The ToxR regulon has been a focus of cholera research for more than three decades. During this time, a model has emerged wherein ToxR functions to activate the expression of Vibrio cholerae virulence factors upon host entry. V. cholerae and other enteric bacteria produce cyclo(Phe-Pro), a cyclic dipeptide that we identified as an inhibitor of V. cholerae virulence factor production. This finding suggested that cyclo(Phe-Pro) was a negative effector of virulence factor production and represented a molecule that could potentially be exploited for therapeutic development. In this work, we investigated the mechanism by which cyclo(Phe-Pro) inhibited virulence factor production. We found that cyclo(Phe-Pro) signaled through ToxR to activate the expression of leuO, a new virulence regulator that functioned to repress virulence factor production. Our results have identified a new arm of the ToxR regulon and suggest that ToxR may play a broader role in pathogenesis than previously known.
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The Cyclic Dipeptide Cyclo(Phe-Pro) Inhibits Cholera Toxin and Toxin-Coregulated Pilus Production in O1 El Tor Vibrio cholerae
Journal of bacteriology, 2010Co-Authors: Xiaowen R. Bina, James E. BinaAbstract:Cyclo(Phe-Pro) is a cyclic dipeptide produced by multiple Vibrio species. In this work, we present evidence that cyclo(Phe-Pro) inhibits the production of the virulence factors cholera toxin (CT) and toxin-coregulated pilus (TCP) in O1 El Tor Vibrio cholerae strain N16961 during growth under virulence gene-inducing conditions. The cyclo(Phe-Pro) inhibition of CT and TCP production correlated with reduced transcription of the virulence regulator tcpPH and was alleviated by overexpression of tcpPH.
Derek G. Smyth - One of the best experts on this subject based on the ideXlab platform.
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The thyrotropin-releasing hormone-like peptides pGlu-Phe-Pro amide and pGlu-Glu-Pro amide increase plasma triiodothyronine levels in the mouse; the activity is sensitive to testosterone
European journal of pharmacology, 1998Co-Authors: Asunción Cremades, Rafael Peñafiel, Victor Rausell, Jesus Del Rio-garcia, Derek G. SmythAbstract:Three naturally occurring peptides, pGlu-Glu-Pro amide, pGlu-Phe-Pro amide and pGlu-Gln-Pro amide, with similar structures to thyrotropin releasing hormone (TRH) have recently been identified but no studies of their in vivo activities have been reported previously. We describe here the ability of pGlu-Phe-Pro amide and pGlu-Glu-Pro amide to influence thyroid status. Subcutaneous administration of these 'TRH-like' peptides in male and female CDI mice led to increased levels of triiodothyronine (T3) and to a lesser extent tetraiodothyronine (T4) in the circulation. pGlu-Phe-Pro amide was more potent than pGlu-Glu-Pro amide; it exhibited a similar potency to pGlu-His-Pro amide (TRH). pGlu-Phe-Pro amide, pGlu-Glu-Pro amide and TRH produced significantly greater effects in the female than in the male. Castration of male mice led to increased activities, with potencies comparable to those seen in the female; in contrast treatment of female mice with testosterone resulted in reduced activities, similar to those observed in the control male. The effects of potassium deprivation on the activities of the TRH-like peptides were also investigated. This diet, which results in decreased testosterone levels in the male, led to increased activities of the TRH-like peptides and TRH, approaching the potencies observed in the female. The results demonstrate that the TRH-like peptides pGlu-Phe-Pro amide and pGlu-Glu-Pro amide which occur naturally in the thyroid gland exhibit biological activity in influencing thyroid status in vivo. The activities are sensitive to testosterone.
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The TRH‐like peptides in rabbit testis are different from the TRH‐like peptide in the prostate
FEBS letters, 1996Co-Authors: Helena Linden, Jesus Del Rio-garcia, Ariana E. Huber, Günther Kreil, Derek G. SmythAbstract:Human seminal fluid contains a number of tripeptide amides with similar structures to thyrotropin releasing hormone (TRH), two of which have been identified as pGlu-Glu-Pro amide and pGlu-Phe-Pro amide. To determine whether these peptides originate in the same tissues and have the same molecular origin, TRH-immunoreactive peptides were extracted from the prostate and testis of the rabbit, purified by ion exchange chromatography and HPLC, and identified by co-chromatography with 3H-labelled marker peptides. In addition, trypsin digestion was used to release TRH-like tripeptides from N-extended forms of these peptides. The sole TRH-like peptide in the prostate was shown to be pGlu-Glu-Pro amide; it was not accompanied by a detectable amount of pGlu-Phe-Pro amide. The prostate also appeared to contain a very small amount of N-extended forms of these peptides. In contrast to the prostate, the testis contained high concentrations of N-extended forms of pGlu-Phe-Pro amide but essentially no tripeptide. The testis also contained N-extended forms of two other neutral TRH-like peptides which were less hydrophobic than pGlu-Phe-Pro amide. Neither the prostate nor the testis contained a significant amount of TRH. The results show that in the rabbit the TRH-like peptides pGlu-Glu-Pro amide and pGlu-Phe-Pro amide occur in different tissues and appear to be formed from different precursors.
