Mass spectrometry study of noncovalent complexes formation of antibiotic cycloserine with N-acetyl-D-glucosamine and ascorbic acid

Abstract

Background: While antibiotic cycloserine (CYS) is widely applied in the treatment of tuberculosis, our knowledge of the drug intermolecular interactions with targeting biomolecules and other drugs remains incomplete. It is believed that the CYS antibacterial activity is related to inhibiting the bacterial cell wall biosynthesis. On the other hand, intermolecular interactions of CYS with ascorbic acid (ASC) molecules is worth of studying taking into account that ASC can be used as supporting vitamin preparation or can be affiliated with the patients nutrition. Objectives: The purpose of the current model study are to examine biologically significant intermolecular interactions of CYS with N-acetyl-D-glucosamine (NAG) as one of the main component of peptidoglycan of bacterial cell wall and to verify the possibility of noncovalent complexes formation between CYS and ASC molecules using electrospray ionization mass spectrometry (ESI MS) technique. Materials and methods: The objects of the study are model systems composed of CYS and NAG or CYS and ASC prepared in a polar methanol solvent for the ESI MS probing. ESI mass spectra are obtained using the approach earlier developed by us for investigation of the noncovalent complexation of drugs with targeting biomolecules. Results: The experiments reveal that the ESI mass spectrum of (CYS–NAG) model system contains peaks of protonated molecular clusters of CYS with NAG: [CYS•NAG•H]+ and [CYS•2NAG•H]+. Existing of such peaks in the spectrum testifies to formation of stable noncovalent complexes between CYS and NAG in the studied solution. ESI MS examining of (CYS–ASC) system reveals the noncovalent pair complexation of CYS and ASC molecules confirmed by the recording of intensive peak of [CYS•ASC•H]+ cluster in the spectrum. Conclusions: The ESI MS findings point to the possibility of noncovalent complexation of CYS with NAG in the polar media including biological systems. Such complexation between the antibiotic and NAG as component of peptidoglycan of bacterial cell wall is considered to be biologically significant for the process of the cell wall biosynthesis inhibiting by CYS. Stable noncovalent complexes formation between the CYS and ASC molecules is suggested as a potential molecular mechanism of the drugs activity modulation under their joint usage.