Vemula H, Bobba S, Putty S, Barbara JE, Gutheil WG. Ion-pairing liquid chromatography-tandem mass spectrometry-based quantification of uridine diphosphate-linked intermediates in the Staphylococcus aureus cell wall biosynthesis pathway.
Anal Biochem 2014;
465:12-9. [PMID:
25086364 DOI:
10.1016/j.ab.2014.07.024]
[Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2013] [Revised: 07/22/2014] [Accepted: 07/23/2014] [Indexed: 11/22/2022]
Abstract
Bacterial cell wall biosynthesis is the target of several antibiotics and is of interest as a target for new inhibitor development. The cytoplasmic steps of this pathway involve a series of uridine diphosphate (UDP)-linked peptidoglycan intermediates. Quantification of these intermediates is essential for studies of current agents targeting this pathway and for the development of new agents targeting this pathway. In this study, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for quantification of these intermediates in Staphylococcus aureus. To address the problem of poor retention of UDP-linked intermediates on reverse phase media, an ion-pairing (IP) approach using N,N-dimethylhexylamine was developed. MS/MS detection in negative mode was optimized for UDP-GlcNAc, UDP-MurNAc, UDP-MurNAc-L-Ala, UDP-MurNAc-L-Ala-D-Glu, UDP-MurNAc-L-Ala-D-Glu-L-Lys, and UDP-MurNAc-L-Ala-D-Glu-L-Lys-D-Ala-D-Ala. The lower limits of quantification (LLOQs) for these analytes were 1.8, 1.0, 0.8, 2.2, 0.6, and 0.5 pmol, respectively, which correspond to LLOQs of 6, 3, 3, 7, 2, and 2 nmol/g bacteria, respectively. This method was demonstrated for quantification of in vivo levels of these intermediates from S. aureus (0.3mg dry weight analyzed) treated with fosfomycin, D-boroAla, D-cycloserine, and vancomycin. Metabolite accumulation is consistent with the known targets of these antibiotics and indicates potential regulatory loops within this pathway.
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