Staphylococcus aureus TMPK and TK showing distinct structural differences with human TMPK and TK – A probable explanation in the pathogenesis

Abstract Background The biosynthesis of dTMP in Staphylococcus aureus is catalyzed by thymidine kinase (TK) whose concentration plays critical role in the formation of small colony variants. This dTMP is phosphorylated to dTDP by thymidine monophosphate kinase (TMPK) for subsequent synthesis of dTTP in the bacteria. Owing to the importance of these enzymes in S. aureus TMPK and TK genes were characterized and compared with human TMPK and TK. Method The TMPK and TK genes were PCR amplified from the chromosomal DNA of S. aureus ATCC12600 and cloned, sequenced, expressed and characterized. The annotated protein sequence of TMPK and TK were compared with other bacterial and human TMPK and TK. The S. aureus TMPK and TK structures were retrieved from PDB and compared with human TMPK and TK structures. Results The gene sequences ( FJ415069 and FJ232923 ) showed complete homology with TMPK and TK genes present in all S. aureus strains. The 3D comparative structural analysis between S. aureus and human TMPK and TK showed very close homology between them as indicated from RMSD values of 0.913 A and 1.336 A respectively. However, presence of G in the P-loop region of S. aureus TMPK whereas R was found in human TMPK similarly, absence of KEN box in S. aureus TK and present in human TK. Conclusion S. aureus phosphorylates only L enantiomer of dTMP while human TMPK selectively phosphorylates the D enantiomer of dTMP and its analogs probably explains this enzyme of S. aureus specific target for the development of new antimicrobial agents and conspicuous absence of human TK in active cells probably explains the rapid proliferation of S. aureus in human host.