Team:NCTU Formosa/CSP design

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Carotenoid Pathway

Introduction

This pathway explain how Fernesyl Diphosphate is catalyzed to Zeathaxine by different temperature.There are three color products in the pathway:red Lycopene, orange beta-Carotene and yellow Zeathaxine.(Figure 1.)

Figure 1. The overview of the Carotenoid pathway

Lycopene
Lycopene is a bright red carotenoid pigment but has no Vit A activity . Lycopene is also an important intermediate in the biosynthesis of many carotenoids.

Beta-Carotene
Beta-Carotene is a strong red-orange pigment abundant in plants and fruits. It’s a member of carotenes and it can be distinguished by two beta-rings at both ends of the molecule. beta–Carotene is the most well-known pre-Vit A among all the carotenoids.

Zeaxanthin
Zeaxanthin is one of the two primary xanthophyll carotenoids contained within the retina of the eye. Zeaxanthin provides the primary yellow pigment.

Design

Figure 2. BBa_K539151 on psb3T5 and BBa_K539281 on psb4A5 cotransformed into host cell DH5 α.

The main concept of the Pathway Commander is to control the flux through the metabolic pathway. Therefore, we choose the Carotenoid synthesis Pathway that can easily display different steps in the pathway by different colors.

If E.coli is incubating below 37℃, mRNAs cannot be translated by ribosomes, because temperature-sensitive RBS(ribosome biding site) BBa_K115002 forms the hairpin. A ribosome cannot bind to the RBS so that it cannot translate CrtY BBa_K118008. As a result, the E.coli only can produce CrtE, CrtB and CrtI BBa_K346090 which convert colorless Farnesyl pyrophosphate to red Lycopene.

When the temperature is at 37℃ or higher, the hairpin is denatured so temperature-sensitive RBS BBa_K115002 is activated . CrtY BBa_K118008 is translated, which convert red Lycopene to orange beta-Carotene.

In the other circuit BBa_K539281 we cotransform into. When we increase the temperature to 42℃, the CI proteins BBa_K098997, the repressor of cI regulated promoter BBa_R0051, are fully denatured. Then the cI regulated promoter is activated and CrtZ BBa_I742158 is produced, converting the orange beta-carotene to yellow Zeaxanthin.