Structural basis of APH(3')-IIIa-mediated resistance to N1-substituted aminoglycoside antibiotics.
Butirosin is unique among the naturally occurring aminoglycosides, having a substituted amino group at position 1 (N1) of the 2-deoxystreptamine ring with an (S)-4-amino-2-hydroxybutyrate (AHB) group. While bacterial resistance to aminoglycosides can be ascribed chiefly to drug inactivation by plasmid-encoded aminoglycoside-modifying enzymes, the presence of an AHB group protects the aminoglycoside from binding to many resistance enzymes, and hence, the antibiotic retains its bactericidal properties. Consequently, several semisynthetic N1-substituted aminoglycosides, such as amikacin, isepamicin, and netilmicin, were developed. Unfortunately, butirosin, amikacin, and isepamicin are not resistant to inactivation by 3'-aminoglycoside O-phosphotransferase type IIIa [APH(3')-IIIa]. We report here the crystal structure of APH(3')-IIIa in complex with an ATP analog, AMPPNP [adenosine 5'-(beta,gamma-imido)triphosphate], and butirosin A to 2.4-A resolution. The structure shows that butirosin A binds to the enzyme in a manner analogous to other 4,5-disubstituted aminoglycosides, and the flexible antibiotic-binding loop is key to the accommodation of structurally diverse substrates. Based on the crystal structure, we have also constructed a model of APH(3')-IIIa in complex with amikacin, a commonly used semisynthetic N1-substituted 4,6-disubstituted aminoglycoside. Together, these results suggest a strategy to further derivatize the AHB group in order to generate new aminoglycoside derivatives that can elude inactivation by resistance enzymes while maintaining their ability to bind to the ribosomal A site.
Department of Biochemistry, McGill University, 3649 Promenade Sir William Osler, Montreal, Quebec, Canada.
Desiree H
DH
Fong
Albert M
AM
Berghuis
D000583:Amikacin / Q000737:chemistry; D000617:Aminoglycosides / Q000737:chemistry* / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects*; D002076:Butirosin Sulfate / Q000737:chemistry; D018360:Crystallography, X-Ray; D024881:Drug Resistance, Bacterial; D019868:Kanamycin Kinase / Q000737:chemistry*; D008958:Models, Molecular; D011485:Protein Binding; D017433:Protein Structure, Secondary
D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D002076:Butirosin Sulfate; D000583:Amikacin; D019868:Kanamycin Kinase