Difference between revisions of "Part:BBa K4324100"

Revision as of 14:46, 1 October 2022

NAD(P)H-dependent D-xylose reductase from S. stipitis

XR is an enzyme that serves as a catalyst for the conversion of xylose into xylitol, and vice versa, according to the following chemical equation: D-xylose + NAD(P)H + H+ ⇌ xylitol + NAD(P)+

In S. stipitis yeast cells, XR forms the first process in the XR-XDH pathway, which converts xylose into xylulose via xylitol. Xylulose is then converted into xylulose-5-phosphate (X5P) for further metabolism in the pentose phosphate pathway.

E. coli do not exhibit the XR-XDH pathway, instead having an XI pathway which directly converts xylose into xylulose. Hence, together with xylitol dehydrogenase (XDH) which can convert xylitol to xylulose, XR presents an alternate xylose metabolism pathway for E. coli.

Furthermore, as the reaction from xylose to xylitol is reversible, this part enables E. coli to utilise xylitol as an energy source through its conversion to xylose, which then follows the XI pathway.

Usage

Our project focused on the improvement of xylose utilisation in E. coli. One part of this process was to incorporate a yeast-derived XR-XDH pathway

Biology

Figure 1 Xylose metabolism pathways of various microorganisms, from Biochemical routes for uptake and conversion of xylose by microorganisms by Zhao, Z., Xian, M., Liu, M. et al.

Xylose reductase is an enzyme that serves as a catalyst for the conversion of xylose into xylitol, and vice versa, according to the following chemical equation:

In S. stipitis yeast cells, XR forms the first process in the XR-XDH pathway, which converts xylose into xylulose via xylitol. Xylulose is then converted into xylulose-5-phosphate (X5P) for further metabolism in the pentose phosphate pathway.

E. coli do not exhibit the XR-XDH pathway, instead having an XI pathway which directly converts xylose into xylulose. Hence, together with xylitol dehydrogenase (XDH) which can convert xylitol to xylulose, XR presents an alternate xylose metabolism pathway for E. coli.

Furthermore, as the reaction from xylose to xylitol is reversible, xylose reductase enables E. coli to utilise xylitol as an energy source through its conversion to xylose, which then follows the XI pathway.

Characterisation

Sequence and Features