Part:BBa_K3570011

CrtYB(ek)I - Tridomain fusion protein for β-carotene production in yeast

Assembly Compatibility:

10
COMPATIBLE WITH RFC[10]
12
COMPATIBLE WITH RFC[12]
21
INCOMPATIBLE WITH RFC[21]
Illegal BglII site found at 2289
Illegal XhoI site found at 3868
23
COMPATIBLE WITH RFC[23]
25
COMPATIBLE WITH RFC[25]
1000
INCOMPATIBLE WITH RFC[1000]
Illegal BsaI site found at 1068
Illegal BsaI site found at 3193
Illegal BsaI.rc site found at 1399
Illegal SapI site found at 2593

Usage

Nowadays, the supplement of food in vitamins is done routinely. New biotechnological processes are developed in order to allow cheaper, faster, and more accessible production of vitamins. The functional goal of this part is to enrich Saccharomyces Cerevisiae in β-carotene.

The biosynthetic pathway from geranylgeranyl diphosphate (GGPP) to β-carotene consists of only two enzymes CrtYB and CrtI from Xanthophyllomyces dendrorhous. These enzymes have other enzymatic activities which lead to multiple side-products on the way to β-carotene (fig. 1). Side-products are synthesized mainly because CrtYB and CrtI are spatially distant from each other. CrtYB is a transmembrane protein while CrtI is in the cytosol. Fusing CrtYB and CrtI would allow a higher yield of β-carotene production. See “Biology” part to get more details.

Biology

Biosynthesis of β-carotene in X. dendrorhous begins with the production of phytoene from GGPP by the domain B of bifunctional lycopene cyclase/phytoene synthase (CrtYB). Phytoene desaturase (CrtI) then catalyzes four successive desaturation reactions to form lycopene. In the end, the domain Y of CrtYB performs the cyclization on both sides of lycopene to produce β-carotene (fig.1).

Fig. 1: From Rabeharindranto et al. 2019. Presumed biosynthetic pathway for the synthesis of β-carotene in X. dendrorhous (Verdoes et al., 1999). The bifunctional lycopene cyclase/phytoene synthase (CrtYB) enzyme is depicted in orange, the phytoene desaturase enzyme (CrtI) is depicted in red. Orange or red boxes represent the localization of the modifications introduced by the CrtYB or CrtI enzymes respectively.

Eukaryotic CrtY enzymes are predicted to be transmembrane proteins. On the contrary, CrtB and possibly CrtI are supposedly cytosolic (Schaub et al., 2012). Additionally, in some fungi, the phytoene CrtY and CrtB catalytic activities are fused within a multidomain protein named CrtYB in Xanthophyllomyces dendrorhous (Verdoes et al., 1999). The complete biosynthetic pathway of X. dendrorhous, with a multidomain CrtYB, was efficiently expressed in S. cerevisiae (Verwaal et al., 2007). Even though this heterologous system is the most productive to date, the accumulation of β-carotene precursors in the pathway, such as phytoene, was remarked. Nevertheless, the overexpression of CrtI to overcome the metabolic bottleneck turned out to be only partially successful (Verwaal et al., 2007).

Recently, the natural tridomain fusion (CrtIBY) from Schizotrium sp. was expressed in Yarrowia lipolytica (Gao et al., 2017) but unfortunately, the β-carotene production yields were considerably lower than those obtained with the yeast-expressed X. dendrorhous configuration (Verwaal et al., 2007; Xie et al., 2015). We then searched to design an enzyme(s), that would have at the same time high production yields of β-carotene precursors (as in X. dendrorhous) with the spatial proximity of both cytosolic enzymes (CrtB and CrtI).

A strategy for creating an enzyme that would have crtYB et crtI activities and every listed property above was adapted from Rabeharindranto, H et al., 2019. This way, a tridomain fusion protein CrtYBekI was expressed in S. cerevisiae, with ‘‘ek’’ being a peptidic linker. This spatial reorganization of the carotenoid enzymes should reduce the accumulation of intermediates and reorient the metabolic fluxes towards β-carotene production.

Experiments

Team iGEM Toulouse 2020 did not have sufficient time to complete the cloning and hence, to test this part functionality.

Related parts on registry

There is a certain number of parts, already present on the registry, that are corresponding to single-enzymes such as CrtI (BBa_K2407309), CrtYB (BBa_K2407311, BBa_K530000) or CrtY (BBa_K539119, BBa_J29030, BBa_I742154, BBa_K118008). The main difference consists in the sequence of the proteins, which is taken from other organisms and are remarkably different. Also, the usage of protein of fusion as presented here, is believed to enhance the carotenoid production compared to the usage of two enzymes separately (Rabeharindranto, H et al., 2019).

References