Biosynthetic Mechanism forL-Gulose in Main Polar Lipids ofThermoplasma acidophilumand Possible Resemblance to Plant Ascorbic Acid Biosynthesis

Abstract

L-Gulose is a very rare sugar, but appears as a sugar component of the main polar lipids characteristic in such a thermophilic archaeon as Thermoplasma acidophilum that lives without cell walls in a highly acidic environment. The biosynthesis of L-gulose in this thermophilic organism was investigated with deuterium-labeling experiments. L-Gulose was found to be biosynthesized from D-glucose via stepwise stereochemical inversion at C-2 and C-5. The involvement of an epimerase related to GDP-mannose 3,5-epimerase, the key enzyme of plant ascorbate biosynthesis, was also suggested in this C-5 inversion. The resemblance of Lgulose biosynthesis in archaea and plants might be suggested from these results.

GDP-altrose as novel product of GDP-mannose 3,5-epimerase: Revisiting its reaction mechanism

“…Furthermore, L-gulose shows potential as building block of L-nucleoside-based antiviral and anticancer medications [34,35]. Besides, L-gulose was found to be a component of the main polar lipids of Thermoplasma acidophilum, where it might mediate in the organism's extremophile properties [36]. In addition, the elimination of C5epimerization would unlock the possibility of GDP-D-altrose production and allow the evaluation of the sugar's application potential.…”

GDP-Mannose 3,5-Epimerase: A View on Structure, Mechanism, and Industrial Potential

“…An example of a natural l -guloside is the main polar lipid of Thermoplasma acidophilum . Also here, the biosynthesis route for the activated l -gulose is expected to pass over an GM35E or homologous enzyme ( Yamauchi and Nakayama, 2013 ). These natural sources of l -Gal and l -Gul could also be interesting targets to search for novel GM35E’s and/or GT enzymes that would be able to utilize GM35E’s products as substrate for glycoside production.…”

Advances in Novel Animal Vitamin C Biosynthesis Pathways and the Role of Prokaryote-Based Inferences to Understand Their Origin

“…They differ, however, in the molecular mechanisms that lead to this step, as in the characterized animal pathway this molecule derives from D-Glucuronate and in plants from L-Gulose [ 146 , 147 ]. The metabolism of L-Gulose seems to be restricted to plants and archaea species [ 148 ], since the formation of L-Gulose likely involves a reaction catalyzed by a GDP-Mannose 3′,5′-Epimerase (GME) [ 107 , 148 , 149 , 150 ], and such epimerase activity was only found associated with the conversion of GDP-D-Mannose to GDP-L-Galactose in animals [ 151 ]. Considering these observations, and that naturally occurring L-Gulose is considerably rare [ 152 ], VC synthesis in B. mori likely does not rely on this precursor, and thus the nomenclature referred to in [ 116 ] should be interpreted with caution.…”