Crystal Structure of the N-Acetylmuramic Acid α-1-Phosphate (MurNAc-α1-P) Uridylyltransferase MurU, a Minimal Sugar Nucleotidyltransferase and Potential Drug Target Enzyme in Gram-negative Pathogens.

The N-acetylmuramic acid α-1-phosphate (MurNAc-α1-P) uridylyltransferase MurU catalyzes the synthesis of uridine diphosphate (UDP)-MurNAc, a crucial precursor of the bacterial peptidoglycan cell wall. MurU is part of a recently identified cell wall recycling pathway in Gram-negative bacteria that bypasses the general de novo biosynthesis of UDP-MurNAc and contributes to high intrinsic resistance to the antibiotic fosfomycin, which targets UDP-MurNAc de novo biosynthesis. To provide insights into substrate binding and specificity, we solved crystal structures of MurU of Pseudomonas putida in native and ligand-bound states at high resolution. With the help of these structures, critical enzyme-substrate interactions were identified that enable tight binding of MurNAc-α1-P to the active site of MurU. The MurU structures define a "minimal domain" required for general nucleotidyltransferase activity. They furthermore provide a structural basis for the chemical design of inhibitors of MurU that could serve as novel drugs in combination therapy against multidrug-resistant Gram-negative pathogens.