Structural and unfolding features of HlyT, a tetrameric LysR type transcription regulator of Vibrio cholerae

LysR-type transcriptional regulators: state of the art

The LysR-type transcriptional regulators (LTTRs) are DNA-binding proteins present in bacteria, archaea, and in algae. Knowledge about their distribution, abundance, evolution, structural organization, transcriptional regulation, fundamental roles in free life, pathogenesis, and bacteria-plant interaction has been generated. This review focuses on these aspects and provides a current picture of LTTR biology.

Effect of ZnO quantum dots on Escherichia coli global transcription regulator: A molecular investigation

ZnO quantum dots (QDs) are very well known for their antimicrobial activity against several bacteria, however, we still do not know any protein targets of ZnO QDs. In order to determine possible protein target, interaction of ZnO QDs was studied with CRP (Cyclic AMP Receptor Protein), a global transcription regulator protein. Binding between ZnO QDs and E. coli CRP was mainly studied by isothermal titration calorimetry (ITC), structural changes of protein were monitored by fluorescence and circular dichroism spectroscopy, and in-vitro transcription assay was used to asses CRP activity. Result shows that both electrostatic and hydrophobic interactions are involved in CRP-ZnO binding. Different spectroscopic investigation revealed that ZnO binding to CRP leads to extensive unfolding and destabilization, which ultimately leads to protein aggregation. It was also observed that in presence of ZnO dimerization ability of CRP was sharply reduced. In-vitro transcription assay also shows that CRP activity gets severely compromised on ZnO binding. All our data suggests that ZnO QD binding to CRP and consequent structural and functional changes most probably plays a crucial role in ZnO QD induced antimicrobial action.

Metal homeostasis in bacteria: the role of ArsR-SmtB family of transcriptional repressors in combating varying metal concentrations in the environment

Bacterial infections cause severe medical problems worldwide, resulting in considerable death and loss of capital. With the ever-increasing rise of antibiotic-resistant bacteria and the lack of development of new antibiotics, research on metal-based antimicrobial therapy has now gained pace. Metal ions are essential for survival, but can be highly toxic to organisms if their concentrations are not strictly controlled. Through evolution, bacteria have acquired complex metal-management systems that allow them to acquire metals that they need for survival in different challenging environments while evading metal toxicity. Metalloproteins that controls these elaborate systems in the cell, and linked to key virulence factors, are promising targets for the anti-bacterial drug development. Among several metal-sensory transcriptional regulators, the ArsR-SmtB family displays greatest diversity with several distinct metal-binding and nonmetal-binding motifs that have been characterized. These prokaryotic metolloregulatory transcriptional repressors represses the expression of operons linked to stress-inducing concentrations of metal ions by directly binding to the regulatory regions of DNA, while derepression results from direct binding of metal ions by these homodimeric proteins. Many bacteria, e.g., Mycobacterium tuberculosis, Bacillus anthracis, etc., have evolved to acquire multiple metal-sensory motifs which clearly demonstrate the importance of regulating concentrations of multiple metal ions. Here, we discussed the mechanisms of how ArsR-SmtB family regulates the intracellular bioavailability of metal ions both inside and outside of the host. Knowledge of the metal-challenges faced by bacterial pathogens and their survival strategies will enable us to develop the next generation drugs.

Structure and activity of lysozyme on binding to ZnO nanoparticles

The interaction between ZnO nanoparticles (NPs) and lysozyme has been studied using calorimetric as well as spectrophotometric techniques, and interpreted in terms of the three-dimensional structure. The circular dichroism spectroscopic data show an increase in alpha-helical content on interaction with ZnO NPs. Glutaraldehyde cross-linking studies indicate that the monomeric form occurs to a greater extent than the dimer when lysozyme is conjugated with ZnO NPs. The enthalpy-driven binding between lysozyme and ZnO possibly involves the region encompassing the active site in the molecule, which is also the site for the dimer formation in a homologous structure. The enzyme retains high fraction of its native structure with negligible effect on its activity upon attachment to NPs. Compared to the free protein, lysozyme-ZnO conjugates are more stable in the presence of chaotropic agents (guanidine hydrochloride and urea) and also at elevated temperatures. The possible site of binding of NP to lysozyme has been proposed to explain these observations. The stability and the retention of a higher level of activity in the presence of the denaturing agent of the NP-conjugated protein may find useful applications in biotechnology ranging from diagnostic to drug delivery.