Co-evolution of RNA polymerase with RbpA in the phylum Actinobacteria

Dual role of MsRbpA: transcription activation and rescue of transcription from the inhibitory effect of rifampicin

MsRbpA is an RNA polymerase (RNAP) binding protein from Mycobacterium smegmatis. According to previous studies, MsRbpA rescues rifampicin-induced transcription inhibition upon binding to the RNAP. Others have shown that RbpA from Mycobacterium tuberculosis (MtbRbpA) is a transcription activator. In this study, we report that both MsRbpA and MtbRbpA activate transcription as well as rescue rifampicin-induced transcription inhibition. Transcription activation is achieved through the increased formation of closed RNAP-promoter complex as well as enhanced rate of conversion of this complex to a stable transcriptionally competent RNAP-promoter complex. When a 16 aa peptide fragment (Asp 58 to Lys 73) was deleted from MsRbpA, the resulting protein showed 1000-fold reduced binding with core RNAP. The deletion results in abolition of transcription activation and rescue of transcription from the inhibitory effect of rifampicin. Through alanine scanning of this essential region of MsRbpA, Gly 67, Val 69, Pro 70 and Pro 72 residues are identified to be important for MsRbpA function. Furthermore, we report here that the protein is indispensable for M. smegmatis, and it appears to help the organism grow in the presence of the antibiotic rifampicin.

Proteomic analysis of Streptomyces coelicolor in response to Ciprofloxacin challenge

Multi-drug tolerance is an important phenotypic property that complicates treatment of infectious diseases and reshapes drug discovery. Hence a systematic study of the origins and mechanisms of resistance shown by microorganisms is imperative. Since soil-dwelling bacteria are constantly challenged with a myriad of antibiotics, they are potential reservoirs of resistance determinants that can be mobilized into pathogens over a period of time. Elucidating the resistance mechanisms in such bacteria could help future antibiotic discoveries. This research is a preliminary study conducted to determine the effects of ciprofloxacin (CIP) on the intrinsically resistant Gram-positive soil bacterium Streptomyces coelicolor. The effect was investigated by performing 2-DE on total protein extracts of cells exposed to sub-lethal concentrations of ciprofloxacin as compared to the controls. Protein identification by MALDI-TOF/TOF revealed 24 unique differentially expressed proteins, which were statistically significant. The down-regulation of proteins involved in carbohydrate metabolism indicated a shift in the cell physiology towards a state of metabolic shutdown. Furthermore, the observed decline in protein levels involved in transcription and translation machinery, along with depletion of enzymes involved in amino acid biosynthesis and protein folding could be a cellular response to DNA damage caused by CIP, thereby minimizing the effect of defective and energetically wasteful metabolic processes. This could be crucial for the initial survival of the cells before gene level changes could come into play to ensure survival under prolonged adverse conditions. These results are a first attempt towards profiling the proteome of S. coelicolor in response to antibiotic stress. This article is part of a Special Issue entitled: Trends in Microbial Proteomics.

BIOLOGICAL SIGNIFICANCE

Soil-dwelling bacteria could serve as a reservoir of resistance determinants for clinically important bacteria. In this work, we investigated, for the first time, the differential proteomic profile of S. coelicolor cells in response to sub-inhibitory concentrations of Ciprofloxacin using 2-DE. Results indicate a shift in the cell physiology towards a state of metabolic shutdown, possibly to counter the DNA damage by ciprofloxacin. Further, up-regulation of GAPDH, RNA pol mRNA and Translation IF2 protein indicates a reprogramming of the cell for long-term survival. This study could serve as a basis for further investigations to elucidate the general mechanism by which soil bacteria exhibit resistance to fluroquinolones. This may help in developing new drug protocols and inventing novel drugs to counter resistance to this class of antibiotics in pathogenic bacteria.