carotenoids : more than just a pigment

University of Warwick

It is more than just a pigment !

CAROTENOIDS

BIOSYNTHESIS PATHWAYS IN PLANTS

Muhammed Sadiq

2012-09-119

Overview

1. Introduction

2. Chemical structure

3. Functions of carotenoids

4. The carotenoid pathway

5. Insilico analysis

6. Biotechnological

applications

7. Conclusion

8. Reference

Introduction

Carotenoids are 2nd most abundant pigment with more than

750 members.

In 1831 Wackenroder isolated carotene from carrots and in

1837 Berzelius named the yellow pigments from autumn

leaves, xanthophylls.

Carotenoids are C40 lipophilic isoprenoid.

β-Carotene supplements are widely used as oral sun

protectants

***Why some ripen fruits shows

green color?

Chemical structure

Carotenoids are tetraterpenoids, 40C, built from four terpene

units each containing 10 carbon atoms

Backbone contain 15 conjugated double bonds

Carbon units are linked by alternating single and double bonds.

Amount of conjugated double bond changes wavelength of light

it can absorb, vary in colors from red, orange and yellow

Structure of common carotenoids

Oxygenated carotenoids are termed as xanthophylls.

Carotenoids structures containing fewer than 40 carbon atoms --

- Apocarotenoids.

Oxidative degradation and enzymatic cleavage changes flavor

and nutritional quality.

Apocarotenoids

Cleavage products of parent carotenoids. (CCD)

ABA - from 9-cis-violoxanthin and 9-cis-neoxanthin

Strigolactones.

β - ionone

In animals vitamin A and its derivatives (retinoids).

Functions of carotenoids

In chloroplast and chromoplast

Biological properties

Chloroplast

Carotenoids absorb light in blue region of the spectrum (400

to 600 nm), transferred to chlorophylls.

Singlet to singlet transfer

Quenching excess light in the form of chlorophyll triplet state

energy transfer

Zeaxanthin prevent lipid peroxidation through out thylakoid

membrane.

Transfer as vibrational heat into the surrounding medium.

Carotenoids account for ~20-30% of all light harvested

Carotenoids may also serve as conductors of electrons.

Chromoplast

Chromoplasts are carotenoid-containing plastids

Main function of chromoplast carotenoids is the attraction of

pollinating insects and animals.

Acylated xanthophylls required for the formation of chromoplast

structures

Biological properties

Anticarcinogenic effects.

Anti-inflammatory effects.

Radical scavenging

activity.

Antiobesity

Improve visual function

Influences gene expression

and immune function.

Prevention of cardiovascular

disease.

Antioxidant Properties

Stabilization of singlet oxygen by physical and chemical

nature.

Chemical stabilization involves the union between the

carotenoid and the free radical. In physical, conversion into low

energy state.

Skin protection

Scavenging of reactive oxygen species.

University of Illinois

University of Georgia

Cardiovascular Disease Prevention

LDL oxidation showed β-carotene carried in LDL is oxidized

prior to the onset of oxidation of LDL polyunsaturated fatty

acids

Antiobesity effects

(UCP1) expressed only in BAT , key molecule

Fucoxanthin reduced WAT and promote expression of UCP1

Age-related Macular Degeneration

Macula, or yellow spot, part of the retina and area of

maximum visual.

Lutein, protective effects on macula and prevents cataract

development.

Effects of lutein on AMD - absorbing harmful light,

quenching singlet oxygen and other free radicals

Can beta-carotene cause cancer ?

Free-radical-rich atmosphere produced by the chemicals in cigarette

smoke and the resultant inflammatory response in the lung with

complex secondary reactive oxygen and nitrogen species enhance

the formation of unusual b-carotene oxidant and other reactive

species (Journal of the National Cancer Institute)

Adverse effects of high-dose beta carotene on lung cancer incidence

and overall mortality ... related to the pharmacologic doses of beta

carotene used

The carotenoid pathway

Synthesis of carotenoid precursors

Two isoprene isomers, isopentenyl diphosphate (IPP) and

its allylic isomer dimethylallyl diphosphate (DMAPP).

2 pathways exist for IPP production in plants: MVA and

MEP pathway.

IPP and DMAPP for carotenoid biosynthesis in plants are

from the MEP pathway

MEP pathway uses glyceraldehyde 3-phosphate and

pyruvate as initial substrates to form DXP, catalyzed by

DXS.

MEP is formed by a intermolecular rearrangement and

reduction of DXP by the enzyme DXR

B- Carotene

biosynthesis

Xanthophyll Biosynthesis

IPP isomerase

Catalyses formation of DMAPP from IPP, a reversible

isomerization reaction.

cDNAs for IPP isomerase identified in Arabidopsis, lettuce,

Brassica, cassava, Sweetpotato and number of other plants.

Two distinct cDNAs for this enzyme, Ipp1 and Ipp2, identified

in Arabidopsis.

Yet, no more than two different cDNAs or

genes identified for this enzyme in any plant.

DXS and DXR are important in carotenoid flux

regulation

Both enzymes are encoded by single genes and

rate-determining enzymes.

Synthesis of Geranylgeranyl Pyrophosphate

GGPS catalyzes successive condensation reactions.

Condensation of IPP and DMAPP to form GGPP

Sequential addition of three IPP molecules to DMAPP,

catalyzed by (GGPS), gives 20-carbon molecule GGPP.

GGPP synthase (GGPPS)

Multifunctional enzyme.

Antibodies against GGPPS purified from Capsicum annuum

chromoplasts.

In Arabidopsis, five different cDNA with sequential similarity

to pepper GGPP synthase, identified.

Synthesis of Phytoene

First dedicated step of carotenoid biosynthesis

(PSY) catalyzes conversion of two molecules of GGPP into

prephytoene pyrophosphate (PPPP) and into phytoene.

Two molecules of GGPP are joined by condensation reaction

with loss of hydrogen and diphosphate group, results

phytoene.

First PSY gene(pTOM5) identified from tomato leaves.

Phytoene synthase genes also cloned from plants like maize,

pepper, Arabidopsis and Narcissus etc.

In tomato (PSY1), identified in fruits, PSY2 present in leaves

and PSY3 in roots function under stress condition.

Maize & rice PSY3 – abiotic stress induced ABA formation.

Regulation of PSY

Increase activity of DXS induce PSY expression in potato &

tomato.

PSY is negatively regulated by (P1F1) TF during seed de-

etiolation.

Reduced amount of α-carotene modulate PSY protein levels.

Epigenetic factors.

Desaturation of phytoene

Colorless compound phytoene into yellow, orange, and red

carotenoids

Catalyzed by two related enzymes in plants: phytoene

desaturase and ζ-carotene desaturase.

Carotenoid biosynthesis is redox regulated via carotene

desaturase.

Cyclization of Lycopene

Cyclization of linear carotenoid : one branch leads to β-

carotene and xanthophylls and other to α-carotene and lutein.

Lycopene b-cyclase catalyses formation of bicyclic b-carotene

from lycopene in plants

This enzyme introduces two b-rings at the ends of the linear

lycopene molecule forms β carotene and (ε,β) ring forms α-

carotene and xanthophyll

1 ε-LCY gene identified in Arabidopsis and tomato,

Arabidopsis contains a copy of β-LCY , but two β-LCY

copies, Crtl-B and Cyc-B identified in tomato.

Keto lycopene cyclase relates to capsanthin–capsorubin

synthase of pepper and the neoxanthin synthase of tomato

and potato.

Down regulation of ε-LCY shows enhanced accumulation of

β-carotene, zeaxanthin and violaxanthin.

Cyclic carotenes to xanthophylls

Oxygenated derivatives of carotenes

Cyclic carotenes can be modified by hydroxylation to

generate xanthophyll

Hydroxylation of β carotene yields zeaxanthin.

ZEP hydroxylates β ring of zeaxanthin – antheraxanthin &

violaxanthin --- Neoxanthin by NSY

Two different types of carotenoid hydroxylases

(CHYs)

1. Non-heme di-iron enzymes (BCH type), catalyze

hydroxylation of b rings

2. Cytochrome P450 enzymes (CYP97 type), catalyze

hydroxylation of both b and e rings

Genome-wide search and identified putative candidates for

PSY gene in 34 sequenced plants

Phylogenetic analysis shows PSY evolved independently in

algae as well as monocotyledonous and dicotyledonous plants.

Amino acid motifs in algae and plants are highly conserved.

Study provided a theoretical basis for learning evolutionary

relationships.

Insilico analysis of carotenoid pathway

Identified 67 carotenoid biosynthetic genes in B. rapa,

orthologs of the 47 carotenoid genes in A. thaliana

46 were successfully mapped to the 10 B. rapa chromosomes.

Expression analysis of the carotenoid biosynthetic genes

suggested that their expression levels differed among organs.

Study of carotenoid biosynthetic genes in B. rapa provides

insights into carotenoid metabolic mechanisms of Brassica

crop.

Synthetic carotenoids

Commercially available synthetic carotenoids used as

food colorants,

b-carotene,

b-apo- 8'-carotenal (apocarotenal)

canthaxanthin.

good stability in food applications.

Biotechnological applications

Production of smart crops.

Vitamin, medicine and dietary supplement formulations.

Production of insect resistant plants by introducing β-ionone

Production of Golden rice, Super banana

Production lycopene enriched tomatoes

Conclusion

Carotenoid biosynthesis pathways are extensively studied because

of its diverse functions. Future research will address the key

questions related to the coordinated organization of different

components of carotenoid pathway to assemble ‘‘metabolons’’ in

a known sub organellar location.

Reference

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Thank you