Enzymatic glycosylation of the topical antibiotic mupirocin Prakash Parajuli & Ramesh Prasad Pandey & Anaya Raj Pokhrel & Gopal Prasad Ghimire & Jae Kyung Sohng Received: 30 April 2014 /Revised: 9 July 2014 /Accepted: 10 July 2014 # Springer Science+Business Media New York 2014 Abstract Mupirocin is a commercially available antibiotic that acts on bacterial isoleucyl-tRNA synthetase, thereby inhibiting protein synthesis and preventing bacterial infection. An in vitro glycosylation approach was applied to synthesize glycoside derivatives of mupirocin using different NDP- sugars and glycosyltransferase from Bacillus licheniformis. Ultra pressure liquid chromatography-photo diode array anal- yses of the reaction mixtures revealed the generation of prod- uct peak(s). The results were further supported by high- resolution quadruple time of flight electrospray ionization mass spectrometry analyses. The product purified from the reaction mixture with UDP-D-glucose was subjected to NMR analysis, and the structure was determined to be mupirocin 6- O-β-D-glucoside. Other glycoside analogs of mupirocin were determined based on high-resolution mass analyses. Antibac- terial activity assays against Staphylococcus aureus demon- strated complete loss of antibacterial activity after glucosylation of mupirocin at the 6-hydroxyl position. Keywords Mupirocin glycosides . Bacillus glycosyltransferase . Aminoacyl tRNA synthetases . Bacterial resistance Introduction Mupirocin is a broad-spectrum polyketide antibiotic, effective against primary and secondary skin infections and against methicillin-resistant Staphylococcus aureus (“MRSA”), resis- tant to mainstream antibiotics (penicillin, streptomycin, and methicillin) [14, 15, 20]. Since it was isolated as a major metabolite from Pseudomonas fluorescens NCIMB 10586 [34], different analogs (pseudomonic acids A, B, C, D) were discovered, with pseudomonic acid A being recognized as the major component comprising C 17 monic acid (C 12 +C 5 units), esterified with the C 9 saturated fatty acid, 9-hydroxynonanoic acid [10, 12] (Fig. 1). It shares no structural homology with other antibiotics currently in clinical use, and has been used primarily as an ointment with different brand names (e.g., Bactoderm, Bactroban, mupirocin calcium cream) (http:// www.drugbank.ca/drugs/DB00410) for specific pathogens that frequently cause secondary infections in superficial wounds [14]. MRSA strains are commonly found “superbugs,” resistant to many antibiotics. S. aureus and Streptococcus pyogenes are pathogens commonly causing various skin infections [33] of vulnerable sites, such as post-operative wounds burns, and even minor cuts. However, they can ultimately lead to serious problems, such as bloodstream infections, pneumonia, osteo- myelitis, sepsis, and endocarditis (http://mrsa-research-center. bsd.uchicago.edu/patients_families/faq.html). Dealing with these bacteria has become an increasing challenge due to the emergence of resistant variants [29]. Mupirocin provided a solution to this, with activity against aminoacyl tRNA- synthetase. Mupirocin acts as an inhibitor of isoleucyl-tRNA synthe- tase (IleRS) and ultimately blocks the synthesis of essential bacterial proteins, reducing cell sustainability under both in vitro and infectious conditions [20, 29, 30]. This enzyme has established functions and serves as a global regulator of transcription, translation, and various cell signaling pathways whose inhibition is the major target in the rational design of antibacterial agents and new-generation drugs [5, 20]. Mupirocin has been in clinical use since 1985, demonstrating predominant action against Gram-positive pathogens. It is currently the world’ s most widely used antibiotic for control P. Parajuli : R. P. Pandey : A. R. Pokhrel : G. P. Ghimire : J. K. Sohng (*) Institute of Biomolecule Reconstruction, Department of Pharmaceutical Engineering, Sun Moon University, 100 Kalsan-ri, Tangjeonmyun, Asan-si, Chungnam 336-708, Korea e-mail: sohng@sunmoon.ac.kr Glycoconj J DOI 10.1007/s10719-014-9538-6