A novel glucose 6-phosphate isomerase from Listeria monocytogenes

Area of Science:

• Biochemistry
• Microbiology
• Enzymology

Background:

• D-Arabinose 5-phosphate isomerases (APIs) are crucial for D-arabinose 5-phosphate (A5P) metabolism, an intermediate in lipopolysaccharide biosynthesis in Gram-negative bacteria.
• Listeria monocytogenes, a Gram-positive pathogen, possesses a gene for a putative API (Q723E8), despite lacking other enzymes for the Kdo pathway.
• The presence of an API in a Gram-positive bacterium suggests a potentially distinct physiological function for A5P.

Purpose of the Study:

• To characterize the enzymatic activity of the putative API, Q723E8, from Listeria monocytogenes.
• To determine the physiological role of Q723E8 in L. monocytogenes.
• To investigate the potential for alternative A5P metabolic pathways in Gram-positive bacteria.

Main Methods:

• Recombinant expression and purification of the Q723E8 protein.
• Enzymatic assays to test for D-arabinose 5-phosphate isomerase (API) activity.
• Enzymatic assays to test for other sugar isomerase activities, including D-glucose 6-phosphate isomerase (GPI).

Main Results:

• Recombinant Q723E8 did not exhibit API activity.
• Q723E8 demonstrated weak D-glucose 6-phosphate isomerase (GPI) activity.
• L. monocytogenes already possesses a well-characterized, likely more efficient, two-domain GPI, suggesting Q723E8's GPI activity may be redundant.

Conclusions:

• The enzyme Q723E8 from L. monocytogenes is a novel, albeit weak, D-glucose 6-phosphate isomerase (GPI), not an API.
• The weak GPI activity and the presence of another GPI suggest glucose metabolism is unlikely the primary physiological role of Q723E8.
• Further research is needed to elucidate the true function of Q723E8 in L. monocytogenes.