Regulation of AMP deaminase by phosphoinositides.
AMP deaminase (AMPD) converts AMP to IMP and is a diverse and highly regulated enzyme that is a key component of the adenylate catabolic pathway. In this report, we identify the high affinity interaction between AMPD and phosphoinositides as a mechanism for regulation of this enzyme. We demonstrate that endogenous rat brain AMPD and the human AMPD3 recombinant enzymes specifically bind inositide-based affinity probes and to mixed lipid micelles that contain phosphatidylinositol 4,5-bisphosphate. Moreover, we show that phosphoinositides specifically inhibit AMPD catalytic activity. Phosphatidylinositol 4,5-bisphosphate is the most potent inhibitor, effecting pure noncompetitive inhibition of the wild type human AMPD3 recombinant enzyme with a K(i) of 110 nM. AMPD activity can be released from membrane fractions by in vitro treatment with neomycin, a phosphoinositide-binding drug. In addition, in vivo modulation of phosphoinositide levels leads to a change in the soluble and membrane-associated pools of AMPD activity. The predicted human AMPD3 sequence contains pleckstrin homology domains and (R/K)X(n)(R/K)XKK sequences, both of which are characterized phosphoinositide-binding motifs. The interaction between AMPD and phosphoinositides may mediate membrane localization of the enzyme and function to modulate catalytic activity in vivo.
Sims
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Departments of Neurobiology and Cell Biology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA.
Mahnke-Zizelman
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DK
Profit
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AA
Prestwich
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GD
Sabina
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RL
Theibert
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AB
D000659:AMP Deaminase / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D001921:Brain / Q000201:enzymology*; D004789:Enzyme Activation; D006801:Humans; D008969:Molecular Sequence Data; D010716:Phosphatidylinositols / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D016415:Sequence Alignment; D013379:Substrate Specificity
D010716:Phosphatidylinositols; D000659:AMP Deaminase