W0047

Toward Better Antibiotics: New Directions in DD-Peptidase Inhibitors. Nicholas R. Silvaggi, William M. Matousek, Judith A. Kelly, Dept. of Molecular and Cell Biology and Inst. for Materials Science, Univ. of Connecticut, Storrs, CT 06269-3125.

This work, using data collected at Brookhaven National Laboratory, NSLS Beamlines X12B and X12C, describes ultra-high (~1.1Å) resolution X-ray crystal structures of the 37.5kDa Streptomyces R61 D-ala-D-ala carboxypeptidase/transpeptidase (DD-peptidase) complexed with several novel DD-peptidase inhibitors. These structures provide valuable information about the modes of action of these exciting compounds.

Almost all eubacteria require a rigid peptidoglycan cell wall for survival. DD-peptidases are β-lactam-sensitive enzymes that catalyze the final peptidoglycan cross-linking step in bacterial cell wall biosynthesis. _-Lactam antibiotics inhibit DD-peptidases because the _-lactam nucleus of the drugs mimics the D-ala-D-ala portion of the natural cell wall substrate. With the DD-peptidases thus inactivated, cells are unable to synthesize proper cell walls and subsequently lyse and die.

Our ultra-high resolution crystal structures show how novel inhibitors of DD-peptidases interact with the R61 enzyme. The first group of structures details the interactions of unique, R61-specific _-lactams before and after reacting with the enzyme. The side chains of these drugs bind identically to the corresponding portions of the natural cell wall peptide. Cyclic phosph(on)ates, the compounds used in the second set of structures, represent an entirely new class of DD-peptidase inhibitor. These molecules are shown to occupy the enzyme active site in unusual and unexpected ways, making them promising lead compounds for drug design. Indeed, these drugs have only three interactions in common with classical DD-peptidase inhibitors.

The continued efficacy of _-lactam antibiotics is threatened by the constant evolution of resistance mechanisms, including bacterial production of _-lactamases, enzymes that inactivate _-lactam drugs. Inhibitors of _-lactamases and/or antibiotics that target DD-peptidases and are insensitive to _-lactamases are desperately needed.