Close-up of hygB (yellow sticks) bound to APH(4)-Ia, showing the high numbers of H-bonds and van der Waals interactions.
In the non-stop fight against infectious agents, many researchers have foregone searching for new antibiotics and instead have turned to older antibiotics that never reached the clinic for one reason or another. The hope is that modern laboratory techniques can convert these existing compounds into more effective drugs. Such a strategy will require a better understanding of the molecular mechanisms of antibiotic resistance, so in this study, the researchers solved the crystal structure of the resistance enzyme aminoglycoside phosphotransferase (4)-Ia in complex with the aminoglycoside hygromycin B at 1.95 Å resolution.
The APH(4)-Ia enzyme hydrogen bonded with hygB through several polar and acidic side chains, and individual alanine substitutions of these residues did not significantly affect APH(4)-Ia activity, indicating that binding affinity is spread across a distributed network. The binding architecture suggests restricted substrate specificity, and indeed, in a test of 14 aminoglycoside compounds, hygB was the only recognized substrate. The researchers also found that APH(4)-Ia was able to utilize either ATP or GTP for phosphoryl transfer.
Together, the tightly-defined hygB interactions and ATP/GTP promiscuity could be exploited in the design of new aminoglycoside antibiotics.
Structure and function of APH(4)-Ia, a hygromycin B resistance enzyme
Peter J. Stogios, Tushar Shakya, Elena Evdokimova, Alexei Savchenko, and Gerard D. Wright
J. Biol. Chem., published online Nov. 17