Crystal Structure of the Zorbamycin-Binding Protein ZbmA, the Primary Self-Resistance Element in Streptomyces flavoviridis ATCC21892

Abstract

<p class="first" id="P1">The bleomycins (BLMs), tallysomycins (TLMs), phleomycin, and zorbamycin (ZBM) are members of the BLM family of glycopeptide-derived antitumor antibiotics. The BLM-producing <i>Streptomyces verticillus</i> ATCC15003 and the TLM-producing <i>Streptoalloteichus hindustanus</i> E465-94 ATCC31158 both possess at least two self-resistance elements, an <i>N</i>-acetyltransferase and a binding protein. The <i>N</i>-acetyltransferase provides resistance by disrupting the metal-binding domain of the antibiotic that is required for activity while the binding protein confers resistance by sequestering the metal-bound antibiotic and preventing drug activation via molecular oxygen. We recently established that the ZBM producer, <i>Streptomyces flavoviridis</i> ATCC21892, lacks the <i>N</i>-acetyltransferase resistance gene and that the ZBM-binding protein, ZbmA, is sufficient to confer resistance in the producing strain. To investigate the resistance mechanism attributed to ZbmA, we determined the crystal structures of apo and Cu(II)-ZBM-bound ZbmA at the high resolutions of 1.90 Å and 1.65 Å, respectively. Comparison and contrast with other structurally characterized members of the BLM-binding protein family revealed key differences in the protein-ligand binding environment that fine-tunes the ability of ZbmA to sequester metal-bound ZBM and supports drug sequestration as the primary resistance mechanism in the producing organisms of the BLM-family of antitumor antibiotics. </p>