Enzymatic characterization of isocitrate dehydrogenase from an emerging zoonotic pathogen Streptococcus suis

Two isocitrate dehydrogenases from a plant pathogen Xanthomonas campestris pv. campestris 8004. Bioinformatic analysis, enzymatic characterization, and implication in virulence

“…Kinetic studies revealed that the K m value of XccIDH1 for NAD þ (225 mM) was higher than its type I NAD þspecific counterparts, such as Pyrococcus furiosus (68.3 mM) [27], Methylococcus capsulatusbut (122 mM) [28], and A. thiooxidans (180 mM) [24], but lower than that observed for NAD þ -IDHs from S. suis (233 mM) [4], Z. mobilis (312 mM) [3], and Hydrogenobacter thermophilus (357 mM) [29]. XccIDH1 showed comparable catalytic efficiency (k cat /K m ) towards NAD þ (0.219 mM À1 s À1 ) when compared to some other type I dimeric NAD þ -IDHs, such as S. suis (0.176 mM À1 s À1 ) [4] andZ. mobilis (0.282 mM À1 s À1 ) [3], suggesting that XccIDH1 is an equally effective bacterial IDH utilizing NAD þ .…”

“…The deduced amino acid sequences of XccIDH1 showed high homology with those of dimeric NAD + ‐specific IDHs from other bacteria, such as Acidithiobacillus thiooxidans (44%) and S . suis (40%) . Besides, sequence alignment showed that residues involved in the coenzyme and substrate binding are strictly conserved among XccIDH1 and its NAD + ‐specific counterparts (Fig.…”

“…thiooxidans (180 μM) , but lower than that observed for NAD + ‐IDHs from S . suis (233 μM) , Z . mobilis (312 μM) , and Hydrogenobacter thermophilus (357 μM) .…”

“…XccIDH1 showed comparable catalytic efficiency ( k cat / K m ) towards NAD + (0.219 µM −1 s −1 ) when compared to some other type I dimeric NAD + ‐IDHs, such as S . suis (0.176 µM −1 s −1 ) and Z . mobilis (0.282 µM −1 s −1 ) , suggesting that XccIDH1 is an equally effective bacterial IDH utilizing NAD + .…”

Metabolic traits of pathogenic streptococci

“…2‐oxoglutarate synthesis by the fragmentary TCA would not only allow generation of additional NADH but also the production of the main precursor for biosynthesis of amino acids of the glutamate family (glutamate, glutamine, arginine, proline). Isocitrate dehydrogenases of S. suis and S. mutans have been biochemically characterized , and mutants in the TCA genes of S. sanguinis SK36 do not show any significant growth defects in chemically defined media . However, the overall knowledge about the role of the fragmentary TCA cycle in streptococci is still limited and its putative contribution to streptococcal fitness especially under in vivo conditions remains to be elucidated.…”