LE BASI MOLECOLARI DEL GUSTO - · PDF fileX B ~ 5.5 Å ~3.5 Å ~ 3 Å ~3...

Gabriella Morini Università degli Studi di Scienze Gastronomiche, Pollenzo (CN)

[email protected]

LE BASI MOLECOLARI

DEL GUSTO

GabriellaMorini, Cortona 12.2.2017

The chemical composition of food

MACRONUTRIENTS ESSENTIAL MICRONUTRIENTS

NON-ESSENTIAL MICRONUTRIENTS

(proteins, lipids, sugars) (vitamins, minerals)

(nutraceuticals, phytochemicals...)

FOOD

TOXIC SUBSTANCES


Function of defense: alkaloids, glycosides, terpens, polyphenols, bitter, astringent, pungent or irritant… Function of attraction: pigments, hormons, flavors (smell and taste).

Secondary metabolites

FUNCTION OF “MESSENGERS”

BIOACTIVE COMPOUNDS PRODUCED BY PLANTS (phytochemicals)


CHEMORECEPTION: the perception system mediated by chemical compounds.

Vision

Smell

Taste

Touch

They are fundamental to drive our decision: to swallow or not

Chemesthetic sensations


CHEMORECEPTION AS “LANGUAGE”

PRECEPT-INVITATION (positive selection)

PROHIBITION (negative selection)

WARNING VARIOUS INFORMATION


http://images.google.it/imgres?imgurl=http://digilander.libero.it/tuttocomputergalatin/base/classe1/italiano/obbligos.gif&imgrefurl=http://digilander.libero.it/tuttocomputergalatin/base/classe1/italiano/italiano9.htm&h=355&w=355&sz=4&hl=it&start=33&usg=__iuAs12jTYh9mOanfh27dcRU_QSM=&tbnid=R4ufG74qhU7i9M:&tbnh=121&tbnw=121&prev=/images%3Fq%3Dsegnali%2Bstradali%26start%3D20%26gbv%3D2%26ndsp%3D20%26hl%3Dit%26sa%3DN

http://images.google.it/imgres?imgurl=http://kidmir.bo.cnr.it/iperstra/element/castmag2/divieto.gif&imgrefurl=http://kidmir.bo.cnr.it/iperstra/element/castmag2/lavoro.html&h=176&w=174&sz=1&hl=it&start=2&usg=__2chXPtX6w2U33Uk_1GhWZDjUsL4=&tbnid=AyDD1itoxEUu2M:&tbnh=100&tbnw=99&prev=/images%3Fq%3Dsegnali%2Bstradali%2Bdivieto%26gbv%3D2%26hl%3Dit

http://images.google.it/imgres?imgurl=http://www.gingergeneration.it/img/fck/pericolo-generico(1).jpg&imgrefurl=http://www.gingergeneration.it/n/patente-b-i-primi-step-e-l-esame-di-teoria-499-n.htm&h=105&w=120&sz=6&hl=it&start=2&usg=__cm5tjxHU9olWws163WF6Z0COQH4=&tbnid=zbgbazsadSOZ6M:&tbnh=77&tbnw=88&prev=/images%3Fq%3Dsegnali%2Bstradali%2Battenzione%26gbv%3D2%26ndsp%3D20%26hl%3Dit%26sa%3DN

http://www.goodearthliveherbs.com/vegetable_page.htm

http://images.google.it/imgres?imgurl=http://bellquel.bo.cnr.it/scuole/serpieri/erbario/immagini erbacee spontanee/Ombrellifere/Daucus carota 3.jpg&imgrefurl=http://bellquel.bo.cnr.it/scuole/serpieri/erbario/immagini erbacee spontanee/Ombrellifere/Daucus carota.htm&h=250&w=250&sz=16&hl=it&start=11&usg=__t9q41JaKKyeIZxNbQbrYdHZbk9s=&tbnid=T9Pjx4uE6rDMIM:&tbnh=111&tbnw=111&prev=/images%3Fq%3DPIANTE%2BVELENOSE%26gbv%3D2%26hl%3Dit

Nutrition state / health

TASTE

Therefore the choice of food according to taste has a function, not only hedonic,

but also biological.

Food selection/positive negative

Evolution / adaptation


Chaudari &, The cell biology of taste, J Cell Biol, (2010), 190, 285-296

Taste qualities, the taste receptors that detect them & examples of natural stimuli


Taste receptors (mainly

GPCRs, so sweet, umami e

bitter receptors) have been

reported in non-gustatory

tissues (like the gut and

the brain).

An ever increasing number

of reports about taste

receptors in non-gustatory

tissues suggest that these

molecules must have

additional functions apart

from taste.

Finger &, Kinnamon Taste isn’t just for taste buds anymore (2011), f1000 Biology Reports 3


Basic physiology of taste

Food tasting involves three steps:

• Generation of a gustatory input in the oral/nasal cavity

• Transmission of the gustatory input to the brain

• Translation of the gustatory input into sensory/hedonic terms


Taste bud structure. Yellow: type I cells, green: type II or receptor cells (subpopulations dedicated to sweet, umami, or bitter stimuli are shown in different green tones), orange: type III or presynaptic cells, gray: type IV or basal cells, blue: perigemmal or type V cells.

Meyerhof, &, Angew.Chem.Int.Ed., 2011, 50, 2220-2242.


synapse

Not clear how the “quality” of the stimuli is specified. GabriellaMorini, Cortona 12.2.2017

Taste bud

Papillae


Papillae are not selective: in a taste bud there are 50-100 taste receptor cells carrying different taste receptors).

Old map of basic tastes


There are fundamentally two types of transmembrane receptors of relevance for taste and smell, differing for the way a signal is translated into the cell:

Ion channels (ionotropic) GP-linked receptors (metabotropic) Ionotropic receptors: change the intracellular concentration of ions Metabotropic receptors: change the intracellular concentration of “second messenger”


The gustatory input involves

• Taste receptors: Sweet

Umami GPCRs linear code

Bitter

Salty Ionic channels linear code

Acidic

• Olfactory receptors: GPCRs (ca 350 in humans), combinatorial code

• Chemesthetic receptors: Ion channels, linear code GabriellaMorini, Cortona

12.2.2017

G Protein Coupled Receptors (GPCRs)


http://www.google.it/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&ved=0ahUKEwjXh-GPqsfSAhXJXBQKHVgGCy4QjRwIBw&url=http%3A%2F%2Fuclaigem2013.tumblr.com%2F&psig=AFQjCNEpwM_91r2tOj02dTUG8B6qiTEzkw&ust=1489076952751274

SWEET TASTE

- Sweet compounds very different in structure (from small molecules to proteins) .

- Easy to be recognized. The foetus recognize as pleasant the sweet taste.

- Almost everybody like it. It is one of the main hedonic factors of food.

- Involved in important social pathologies: diabetes, obesity, caries GabriellaMorini, Cortona

12.2.2017

OCH3

HN

O

NH2

COOH

O

NH

S

O

OO

NK

S

O

O

OSOO

ONaNH

OH

OCH3

OH

OH O

OHOHO

OO

OH

OOH

OHOH

Aspartame

180x (E951)

Saccharin

400x (E954)Cyclamate, sodium salt

30x (E952)

Acesulfame-K

150x ((E950)

O

HO

OOH

OH

HO

HO

O

Cl

Cl

Cl

Sucralose

600x (E955)NHDC

650x (E959)

Thaumatin 3000x (E957)

O OCH3

NH

O

HN

COOH

Neotame 8000x (E961)

Low calorie sweeteners currently authorised in EU: acesulfame-K (E950), aspartame (E951), aspartame-acesulfame salt (E962), cyclamate (E952), neohesperidine DC (E959), saccharin (E954), sucralose (E955), thaumatin (E957), neotame (E961)


The leaves of Stevia rebaudiana (Bertoni) have been known to taste sweet for hundreds of years. Identification of the sweet components of stevia leaves (steviol glycosides, SGs): in 1955 stevioside (STV, a); in the 1970s discovery of eight additional steviol glycosides, with rebaudioside A (REBA, b) being the second most abundant.

All of these compounds have a common aglycone known as steviol and they differ in the number and the types of sugars attached.


A-H … B B …. H-A

Receptor site

Sweet unit

Shallenberger & Acree, 1967 Kier, 1972 AH

X

B

~ 5.5 Å ~3.5 Å

~ 3 Å

~3 Å

Goodman &,1987-94 Aspartame and other tasting

peptides

Temussi &,1978-90 Saccharins (rigid) & Aspartame (flexible)

derivatives

Tinti & Nofre, 1990-2000 Guanidinic sweeteners.

MultiPoint Attachment MPA Suitable for most of sweet

tasting compounds GabriellaMorini, Cortona 12.2.2017

Morini &, “A three-dimensional receptor model for isovanillic sweet derivatives”. J. Chem. Soc. Perkin Trans. 2, 1449-1454, 1998.

- 17 compounds in the training set; - 9 key AA residues; - 8 compounds in the test set.


Morini &, “A general pseudoreceptor model for sweet compounds: a semi-quantitative prediction of binding affinity for sweet tasting molecules”. J. Med. Chem., 45 (20), 4402-4409, 2002.

- 24 compounds in the training set; - 16 key AA residues; - 5 compounds in the test set.


- Class C: Large N-terminal extracellular domain (Venus Fytrap Module)

- Cysteine-rich domain (CRD), interconnects the VFTM to the HD in most family 3 GPCRs

- Heptahelical transmembrane domain responsible for G-protein activation

- These receptors function as dimers (either homodimers or heterodimers)

The sweet taste receptor is a G protein-coupled receptor (class C, or 3).


The attractive taste modalities sweet and umami are mediated by 3 GPCRs: T1R1, T1R2 and T1R3 (genes TAS1R)

T1R2+T1R3 form a heterodimeric sweet taste receptor, able to respond to all sweet taste stimuli tested

T1R1+T1R3 form a heterodimeric umami taste receptor


Different sweet compounds activate the same sweet taste receptor, inferring that there is just one sweet taste receptor.

Possibility to perform in vitro tests to assess the sweetness of compounds.

Before only sensory evaluation, trough tasting.

How does a single receptor complex respond to the wide range of sweet-tasting compounds?

GabriellaMorini, Cortona

12.2.2017

Humans and rodents show differences in their ability to taste certain artificial sweeteners (rodents cannot taste aspartame, NHDC, cylamates, sweet proteins etc.).

Human-rodent sweet receptor chimeras

Sweet-umami chimeric receptors


The three-dimensional structure of the sweet taste receptor it was (and still is) unknown.

Homology modeling involves taking a known sequence with an unknown structure and mapping it against a known structure of one or several similar (homologous) proteins. It would be expected that two proteins of similar origin and function would have reasonable structural similarity. Therefore it is possible to use the known structure as a template for modelling the structure of the unknown structure.

Comparison of the tertiary structures of homologous proteins have shown that three-dimensional structures have been better conserved during evolution than protein primary structures.


Since the year 2000 it is available the three-dimensional structure of the extracellular domain of the metabotropic glutamate receptor (mGluR1), a homodimer with an active site able to bind glutamate in each subunit, which has a certain degree of homology and high similarity with T1Rs.

T1Rs, SWEET AND UMAMI RECEPTORS:


It is possible to derive homology models using mGluR1 as template. The models are semipredictive of the activity (sweetness) and can be used to derive information in the design of new active compounds.

Morini &.“From small sweeteners to sweet proteins: anatomy of the binding sites of the human T1R2-T1R3 receptor”. Journal of Medicinal Chemistry, 2005, 48, 5520. GabriellaMorini, Cortona

12.2.2017

G.E. DuBois, Molecular mechanism of sweetness sensation, Physiology & Behavor 164, (2016), 453-463


UMAMI TASTE:

- The taste of amino acids (in humans only L-glutamate and L-aspartate) signalling the presence of proteins.

- Often defined as the ultimate-taste, but is not true.


The modern era of umami The “new” taste, umami, was identified almost 100 years ago, in 1908, by Dr. Ikeda of Tokyo Imperial University. He had sought to scientifically identify an official fifth taste, which was recognized for centuries in dashi, the kombu- and bonito-based Japanese fish stock. Dashi, meaning “boiled extract,” is the basis of all Japanese boiled dishes and soups.

The sensation generated by L‐monosodium glutamate

(MSG) was different from any other of the four so‐called basic tastes, and Dr. Ikeda dubbed it ‘umami’,

from the Japanese word umai (delicious). GabriellaMorini, Cortona

12.2.2017

O

O

NH2

HOOCNa

O

O

OH

COOH

HOOC

O

NH

OH

COOH

COOH

Other umami tasting compounds

aspartic acid lactic acid succinic acid N-lactoyl glutamic acid

Lys-Gly-Asp-Glu-Glu-Ser-Leu-Ala delicious peptide

(Glu-lac)

Asp-Asp Glu-Glu Asp-Glu


N

NN

N

H2N

OH

OO3PO

OH OH

N

NN

N

OH

OO3PO

OH OH

N

NN

N

NH2

OO3PO

OH OH

GuanosineMonoPhosphate E627

IMP

Umami enhancers: purine 5’-nucleotides

InosineMonoPhosphate E631

GMP


X.Li & al. “Different functional roles of T1R subunits in the heteromeric taste receptors”, PNAS, 2004, 101, 14258-14263.

In vitro tests demonstrated IMP has no effect on sweet taste receptor, therefore has been speculated that it binds to T1R1.


January 24, 2008 Senomyx Announces Issuance of "Sweet and Savory" Patents about compounds able to strongly potentiate sweetness and umaminess.

Dec 2008 X. Li et.al. PNAS 2008;105:20930-20934


A molecular model of T1R1 VFT domain

X. Li et.al. PNAS 2008;105:20930-20934

Glutamate

IMP or GMP


PNAS, 107, 2010, 4752-4757 Receipt of GRAS (Generally Recognized As Safe) regulatory designation for S6973 Sucrose (table sugar) Enhancer

S6973: enhancer sucrose (50% reduction)

-2009, GRAS

-2011 in businnes

-S2383 : enhancer of sucralose (75% reduction)

- in businnes in USA and Sud America GabriellaMorini, Cortona 12.2.2017

X.Li & al. “Molecular mechanism of the sweet taste enhancers”. PNAS, 107, 2010, 4752-4757

A molecular model of T1R2 VFT domain

sucrose S6973


Bitter taste “is assumed” to detect toxins in food: many poisonous substances elicit bitter taste.

Most of the bitter compounds are from plants.

Many bitter compounds in plants have a positive effect on health.

Others are generated during food processing including heating (roasting of coffee, Maillard reaction products of amino acids and sugars and fermentation).

BITTER TASTE:


25 bitter receptors (belonging to GPCRs, called T2Rs) have been identified in humans.


T2R receptors are proteins composed of approximately 290–330 amino acids.

Bitter receptors are somewhat dissimilar, with a sequence identity at the amino acid level of approximately 17–90%.

“ More conserved the structure than the sequence” (Niv)

T2Rs: GPCRs with short N-terminal extracellular domain (similar to class A GPCRs)


DOI:10.1021/acs.jafc.6b04835

BROAD INTERMEDIATE


Single orthosteric binding pocket with overlapping, but individual, contact points. Before entering the binding pocket the agonists transiently occupy a vestibular binding site, which may act as a “specificy filter” for agoinists


Bitter taste is innate; human neonates react with stereotypic rejection responses indicative of a strong negative hedonic effect.

Since bitter taste is generally linked to aversive responses, elevated levels of bitter compounds may lead to rejection of certain food items by the consumers thereby protecting them from ingesting potentially toxic compounds such as alkaloids or cyanogenic glycosides or spoiled food.


Genetic factors


The omnivore dilemma (Rozin)

Power of recognition and memory to guide us away from poisons and toward nutritious plants. This allows humans to inhabit virtually every terrestrial environment on the planet and to codify “traditional diets”. Humans have, in addition to their senses and memory, the advantage of culture, which stores the experience and accumulated wisdom of countless human tasters before us.


Brain is the most important organ of taste

The definition of taste is part of the cultural heritage of human society.

We choose food not “taste” GabriellaMorini, Cortona 12.2.2017

Taste receptors (mainly

GPCRs, so sweet, umami e

bitter receptors) have been

reported in non-gustatory

tissues (like the gut and

the brain).

An ever increasing number

of reports about taste

receptors in non-gustatory

tissues suggest that these

molecules must have

additional functions apart

from taste.

Finger &, Kinnamon Taste isn’t just for taste buds anymore (2011), f1000 Biology Reports 3



Gabriella Morini Università degli Studi di Scienze Gastronomiche, Pollenzo (CN)

[email protected]

LE BASI MOLECOLARI DEL GUSTO - · PDF fileX B ~ 5.5 Å ~3.5 Å ~ 3 Å ~3...

Documents

Transcript of LE BASI MOLECOLARI DEL GUSTO - · PDF fileX B ~ 5.5 Å ~3.5 Å ~ 3 Å ~3...