Search

Bacterial two-component regulatory systems (TCS) play important roles in sensing environmental stimuli and responding to them by regulating gene expression. VbrK/VbrR, a TCS in Vibrio parahaemolyticus, confers resistance to β-lactam antibiotics through activating a β-lactamase gene. Its periplasmic sensor domain was previously suggested to detect β-lactam antibiotics by direct binding. Here, we report a crystal structure of the periplasmic sensing domain of VbrK (VbrKSD) using sulfur-based single-wavelength anomalous diffraction (S-SAD) phasing. Contrary to most bacterial sensor domains which form dimers, we show that VbrKSD is a monomer using size exclusion chromatography coupled with multi-angle light scattering. This observation is also supported by molecular dynamics simulations. To quantify the binding affinity of β-lactam antibiotics to VbrKSD, we performed isothermal titration calorimetry and other biophysical analyses. Unexpectedly, VbrKSD did not show any significant binding to β-lactam antibiotics. Therefore, we propose that the detection of β-lactam antibiotics by VbrK is likely to be indirect via an as yet unidentified mechanism.

In this paper, a modified phase generated carrier (PGC) demodulation technique based on Mach–Zehnder interferometer (MZI) is proposed, the related simulation and experiment results show that this technique can restrain the influence of the time delay between carrier signals and disturbance signals. Combined with 3×3 coupler, the modified PGC technique uses the two of three output signals as fundamental carrier frequency signal and second-harmonic carrier frequency signal by mathematical transformations, and another output is modulated signal, which enable the three signals output simultaneously from the interferometer. Meanwhile, in order to raise further the signal to noise ratio (SNR), the influences of differential-and-cross-multiplying (DCM) and Arctangent (ATAN) between the modified technique and the traditional technique, time delay, and laser sources with different line-width on demodulation effects are discussed. We believe this work will provide some new methods for the technological research in the field of fiber optical communication.