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The protein Glucose-6-Phosphate Dehydrogenase is an enzyme involved in the metabolic pathways of the majority of organisms. Leuconostoc mesenteroides is a Bacilli Gram-positive bacterium that expresses this enzyme.

Function

G6PD plays an important role in the metabolism of L.mesenteroides. Leuconostoc mesenteroides is a facultactively anaerobic micro-organism which metabolizes glucose to generate lactic acid, ethanol but also carbon dioxyde. This glucose metabolic process (glycolysis and pentose phosphate pathway) is catalysed by G6PD. During this process, NADH is synthesised and used in the heterolactic fermentation and the biosynthesis of fatty acids. The protein G6PD also has a role in protecting cells from destruction as it produces the co-factor NADPH which plays a role in protecting cells from reactive oxygen species ^[1].

Genomic context

It is coded by the G6PD gene (1461 nucleotides)^[2].

Catalytic activity

D-glucose 6-phosphate + NAD+ → 6-phospho-D-glucono-1,5-lactone + H+ + NADH^[3]

KM=114 µM for G6PD (with NADP), KM=69 µM for G6PD (with NAD),

KM=8.0 µM for NADP, KM=160 µM for NAD.

Its regulation depends on the concentration of substrate and coenzyme, rate limiting step in pentose phosphate pathway^[4].

Optimum pH for its activity is 5.4 - 8.9.

Evolutionary conservation

The different structures conserved evolutionary can be observed according to the scale following.

Check, as determined by ConSurfDB.

Mutations

Mutagenesis of this enzyme induces catalytic activity loss: more than 200 mutations have been identified. A mutation in a nucleotide in the sequence coding for G6PD leads to disruption of the normal expression of the enzyme, or to a disruption in the amino acid structure of the enzyme which leads to a loss or decrease of catalytic activity toward its substrate.

The most common mutations in the amino acids sequence found that induce a loss of catalytic activity are a substitution of the bold amino acids by another one^[5]:

MVSEIKTLVT FFGG T GDLAK R K LYPSVFNL YKKGYLQKHF AIVGTA R Q AL NDDEFKQLVR DSIKDFTDDQ AQAEAFIEHF SYRAHDVTDA ASYAVLKEAI EEAADKFDID GNRIFYMSVA PRFFGTIAKY LKSEGLLADT GYNRLMIEK P FGTSYDTAAE LQNDLENAFD DNQLFRI D H Y LG K EMVQNIA ALRFGNPIFD AAWNKDYIKN VQVTLSEVLG VEERAGYYDT AGALLDMIQN H TMQIVGWLA MEKPESFTDK DIRAAKNAAF NALKIYDEAE VNKYFVRAQY GAGDSADFKP YLEELDVPAD SKNNTFIAGE LQFDLPRWEG VPFYVRSGKR LAA K QTRVDI VFKAGTFNFG SEQEAQEAVL SIII D PKGAI ELKLNAKSVE DAFNTRTIDL GWTVSDEDKK NTPEP Y ERMI HDTMNGDGSN FADWNGVSIA WKFVDAISAV YTADKAPLET YKSGSMGPEA SDKLLAANGD AWVFKG.

This sequence being the normal protein sequence found in L. mesenteroides.

Structural highlights

Glucose-6-Phosphate Dehydrogenase is formed of a homodimer, so a dimer of two identical subunit. Each is composed of 2 domains, . Depending on several conditions, it can dimerize to form tetramers. Each monomer in the complex has a substrate binding site that binds to G6P, and a catalytic coenzyme binding site that binds to NADP+/NADPH using the Rossman fold.^[6]