The native serine protease proteinase K binds two calcium cations. It has been reported that Ca(2+) removal decreased the enzyme's thermal stability and to some extent the substrate affinity, but has discrepant effects on catalytic activity of the enzyme. Molecular dynamics simulations were performed on the Ca(2+)-bound and Ca(2+)-free proteases to investigate the mechanism by which the calciums affect the structural stability, molecular motions, and catalytic activity of proteinase K. Very similar structural properties were observed between these two forms of proteinase K during simulations; and several long-lived hydrogen bonds and salt bridges common to both forms of proteinase K were found to be crucial in maintaining the local conformations around these two Ca(2+) sites. Although Ca(2+) removal enhanced the overall flexibility of proteinase K, the flexibility in a limited number of segments surrounding the substrate-binding pockets decreased. The largest differences in the equilibrium structures of the two simulations indicate that, upon the removal of Ca(2+), the large concerted motion originating from the Ca1 site can transmit to the substrate-binding regions but not to the catalytic triad residues. In conjunction with the large overlap of the essential subspaces between the two simulations, these results not only provide insight into the dynamics of the underlying molecular mechanism responsible for the unchanged enzymatic activity as well as the decreased thermal stability and substrate affinity of proteinase K upon Ca(2+) removal, but also complement the experimentally determined structural and biochemical data.
A novel method of bionic Morse coding mimicking humpback whale vocal is presented for covert underwater acoustic communication. The complex humpback whale song is translated as bionic Morse codes based on information entropy. The communication signal is made akin to the natural singing of male humpback whales. The intruder can detect the signal but will not be able to recognize the communication signal due to unified resemblance with the natural sound. This novel technique gives an excellent low probability of recognition characteristics. A flawless stealthy underwater acoustic communication has been established which has negligible chances of deciphered with high imperceptibility. Standard mimicry Morse codes have been developed for the characters of the English language and compared with Morse coding. Covert information of one character per second can be watermarked with perfect stealth and clandestine communication. This novel concept has been verified at transmission distance of five km and less than 10−3 Bit Error Rate (BER) is achieved at Signal to Noise Ratio (SNR) down to negative seven dB. Zero BER is attained by estimating the channel by a matching pursuit algorithm and equalizing the errors by virtual time reversal mirror technique.
Six complexes {(3-bdppmapy)(AuCl) 2 } n (1−6; 3-bdppmapy = N,N′-bis(diphenylphosphanylmethyl)-3-aminopyridine and tht = tetrahydrothiophene) were simultaneously formed by the reaction of Au(tht)Cl and 3-bdppmapy in CH 2 Cl 2 followed by infusion with hexane. Complexes 4−6 could be produced independently by volatilizing solvent in air, solidstate heating, or solvothermal reaction. The PPh 2 −Au−Cl moieties extended in different directions, forming Au−Au and Au−Au−Au interactions. Complex 4 could be converted to 5 by heating to 130 °C, with the cleavage of one Au−Au bond, while 5 reverted back to 4 upon exposure to CH 2 Cl 2 vapor over 11 h. This solid-state phase transition could be recycled and was accompanied by a change in solid-state fluorescence, without obvious intensity decay over five cycles. The reason for both the phase transition and difference in photoluminescence is related to the different numbers and strengths of aurophilic interactions in each complex that could be modeled by density functional theory calculations.
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