Abstract
In recent years, there has been a growing interest in teichoic acids as targets for antibiotic drug design against major clinical pathogens such as Staphylococcus aureus, reflecting the disquieting increase in antibiotic resistance and the historical success of bacterial cell wall components as drug targets. It is now becoming clear that β-O-GlcNAcylation of S. aureus wall teichoic acids plays a major role in both pathogenicity and antibiotic resistance. Here we present the first structure of S. aureus TarS, the enzyme responsible for polyribitol phosphate β-O-GlcNAcylation. Using a divide and conquer strategy, we obtained crystal structures of various TarS constructs, mapping high resolution overlapping N-terminal and C-terminal structures onto a lower resolution full-length structure that resulted in a high resolution view of the entire enzyme. Using the N-terminal structure that encapsulates the catalytic domain, we furthermore captured several snapshots of TarS, including the native structure, the UDP-GlcNAc donor complex, and the UDP product complex. These structures along with structure-guided mutants allowed us to elucidate various catalytic features and identify key active site residues and catalytic loop rearrangements that provide a valuable platform for anti-MRSA drug design. We furthermore observed for the first time the presence of a trimerization domain composed of stacked carbohydrate binding modules, commonly observed in starch active enzymes, but adapted here for a poly sugar-phosphate glycosyltransferase.
Highlights
Methicillin-Resistant Staphylococcus aureus (MRSA) is a leading cause of life-threatening nosocomial infections including pneumonia, bacteremia, and surgical wound infections [1]
Β-lactam class antibiotics such as methicillin have been very successful in the treatment of bacterial infections, effectively destroying bacteria by rupturing their cell
We present the first structure of TarS in the presence of donor substrate UDP-GlcNAc, elucidate various features involved in catalysis, and describe a novel trimerization domain composed of tandem carbohydrate binding motifs
Summary
Methicillin-Resistant Staphylococcus aureus (MRSA) is a leading cause of life-threatening nosocomial infections including pneumonia, bacteremia, and surgical wound infections [1]. Rising resistance to vancomycin has forced the use of undesirable alternatives with high cost and dose limitations due to adverse events [2]. Both β-lactam and glycopeptide antibiotics disrupt peptidoglycan crosslinking that eventually weakens the integrity of the bacterial cell wall and leads to lysis. Due to the efficacy and safety profile of β-lactam antibiotics, re-sensitization of MRSA to these drugs is a promising option that entails understanding of complex resistance mechanisms. Recent reports have uncovered the role of wall teichoic acids and their β-O-GlcNAc decorations, in mediating MRSA resistance to β-lactams [4,5], opening new avenues for drug discovery efforts aimed at re-sensitization
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