Binding and inhibition of human spermidine synthase by decarboxylated S-adenosylhomocysteine

Authors

  • Jolita Šečkutė,

    1. Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853
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  • Diane E. McCloskey,

    1. Department of Cellular and Molecular Physiology, Milton S. Hershey Medical Center, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
    2. Department of Pharmacology, Milton S. Hershey Medical Center, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
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  • H. Jeanette Thomas,

    1. Southern Research Institute, Birmingham, Alabama 35205
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  • John A. Secrist III,

    1. Southern Research Institute, Birmingham, Alabama 35205
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  • Anthony E. Pegg,

    1. Department of Cellular and Molecular Physiology, Milton S. Hershey Medical Center, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
    2. Department of Pharmacology, Milton S. Hershey Medical Center, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
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  • Steven E. Ealick

    Corresponding author
    1. Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853
    • 120 Baker Lab, Cornell University, Ithaca, NY 14853-1301
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Abstract

Aminopropyltransferases are essential enzymes that form polyamines in eukaryotic and most prokaryotic cells. Spermidine synthase (SpdS) is one of the most well-studied enzymes in this biosynthetic pathway. The enzyme uses decarboxylated S-adenosylmethionine and a short-chain polyamine (putrescine) to make a medium-chain polyamine (spermidine) and 5′-deoxy-5′-methylthioadenosine as a byproduct. Here, we report a new spermidine synthase inhibitor, decarboxylated S-adenosylhomocysteine (dcSAH). The inhibitor was synthesized, and dose-dependent inhibition of human, Thermatoga maritima, and Plasmodium falciparum spermidine synthases, as well as functionally homologous human spermine synthase, was determined. The human SpdS/dcSAH complex structure was determined by X-ray crystallography at 2.0 Å resolution and showed consistent active site positioning and coordination with previously known structures. Isothermal calorimetry binding assays confirmed inhibitor binding to human SpdS with Kd of 1.1 ± 0.3 μM in the absence of putrescine and 3.2 ± 0.1 μM in the presence of putrescine. These results indicate a potential for further inhibitor development based on the dcSAH scaffold.

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