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Enzymatic Characteristics of a Polyphosphate/ATP-NAD Kinase, PanK, from Myxococcus xanthus

Yoshio Kimura1, Takuya Kamimoto2, Naotaka Tanaka2

  • 1Department of Applied Biological Science, Faculty of Agriculture, Kagawa University, Miki-cho, Kagawa, Japan. kimura@ag.kagawa-u.ac.jp.

Current Microbiology
|November 20, 2019
PubMed

Insights

Myxococcus xanthus NAD kinase (PanK) uses both ATP and polyphosphate (poly(P)) to produce NADP+. This enzyme efficiently generates NADP+ under starvation conditions, utilizing poly(P) as a preferred substrate.

Area of Science:

  • Biochemistry
  • Microbiology
  • Enzymology

Background:

  • NAD kinase is essential for NADP+ production.
  • Myxococcus xanthus is a soil bacterium that forms fruiting bodies and spores during starvation.
  • Polyphosphate (poly(P)) accumulates during early development in M. xanthus.

Purpose of the Study:

  • To characterize the NAD kinase from Myxococcus xanthus (PanK).
  • To investigate the role of polyphosphate (poly(P)) and ATP as phosphoryl donors for PanK.
  • To understand the substrate specificity and regulatory mechanisms of PanK.

Main Methods:

  • Enzyme activity assays using ATP and various poly(P) chain lengths.
  • Site-directed mutagenesis of the GGDGT motif (Thr-90 to Asn).
  • Kinetic analysis (Km and kcat/Km) for ATP and poly(P).

Main Results:

  • M. xanthus PanK functions as a poly(P)/ATP-NAD kinase, utilizing both substrates.
  • PanK shows minimal NADH kinase activity and is inhibited by NADPH.
  • Mutation of Thr-90 significantly impairs poly(P)-dependent activity more than ATP-dependent activity.
  • PanK exhibits higher catalytic efficiency for short-chain poly(P) (poly(P)4) compared to ATP.

Conclusions:

  • M. xanthus PanK is a unique poly(P)/ATP-NAD kinase with specialized roles in NADP+ biosynthesis.
  • The enzyme's preference for poly(P) suggests an important function during starvation-induced development.
  • Thr-90 is critical for efficient poly(P) utilization by PanK.
Keywords:
Myxococcus xanthusNADP+Polyphosphate/ATP-NAD kinase

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