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Tuberculosis is one of the oldest known infectious diseases, responsible for millions of deaths annually around the world. The ability of Mycobacterium tuberculosis (Mtb) to enter into a dormant state has been considered integral to the success of this bacterium as a human pathogen. One of the key systems involved in regulating the entrance into dormancy is the differentially expressed in virulent strain sensor protein (DevS) [(dormancy survival sensor protein (DosS)]. However, the physiological signal for DevS has remained unclear since it was first shown to be a heme‐based sensor with conflicting reports on whether it is a redox or an oxygen sensor. To address this question and provide a better understanding of the electronic properties of this protein, we present here, for the first time, a series of spectroelectrochemistry measurements of the full‐length holo DevS in anaerobic conditions as well as bound to CO, NO, imidazole (Imz), cyanide, and O2. An interesting feature of this protein is its ability to bind Imz even in the ferrous state, implying small‐molecule analogues could be designed as potential regulators. Nonetheless, a midpoint potential (Em) value of +10 mV [vs normal hydrogen electrode (NHE)] for DevS as measured under anaerobic conditions is much higher than the expected cytosolic potential for Mtb or even within stimulated macrophages (~ −270 mV vs NHE), indicating this sensor works in a reduced ferrous state. These data, along with the high oxygen affinity and very slow auto‐oxidation rate of DevS, provides evidence that it is not a redox sensor. Overall, this study validates the biological function of DevS as an oxygen sensor directly involved in the dormancy/latency of Mtb. [ABSTRACT FROM AUTHOR]

A major challenge to the control and eventual eradication of Mycobacterium tuberculosis infection is this pathogen's prolonged dormancy. The heme‐based oxygen sensor protein DevS (DosS) plays a key role in this phenomenon, because it is a major activator of the transcription factor DevR. When DevS is active, its histidine protein kinase region is ON and it phosphorylates and activates DevR, which can induce the transcription of the dormancy regulon genes. Here, we have investigated the mechanism by which the ligation of molecular oxygen to a heme‐binding domain in DevS switches OFF its histidine protein kinase region. To shed light on the oligomerization states of this protein and possible protein‐surfaces of interaction, we used analytical gel filtration, together with dynamic light scattering, fluorescence spectroscopy and chemical crosslinking. We found that DevS exists as three major species: an octamer, a tetramer and a dimer. These three states were observed for the concentration range between 0.5 and 20 μm DevS, but not below 0.1 μm. Levels of DevS in M. tuberculosis are expected to range from 5 to 26 μm. When this histidine protein kinase was OFF, the DevS was mainly tetrameric and dimeric; by contrast, when the kinase was ON, the protein was predominantly octameric. The changes in quaternary structure were rapid upon binding to the physiological signal. This finding represents a novel strategy for switching the activity of a two‐component heme‐based sensor. An enhanced understanding of this process might potentially lead to the design of novel regulatory agents that target the multimer interfaces for treatment of latent tuberculosis. The oxygen sensor DevS (DosS) of Mycobacterium tuberculosis is found as a mixture of oligomers. There is a rapid change in the quaternary structure of this protein upon binding to the physiological signal. In the inactive state, DevS bound to oxygen is mainly in the dimer and tetramer states. However, in the active state, in anaerobic conditions, DevS is found mainly as an octamer, which may be responsible for the activity of the protein. [ABSTRACT FROM AUTHOR]

A lectin from seeds of Dioclea lasiocarpa (DLL) was purified in a single step by affinity chromatography in a Sephadex G-50 column. DLL haemagglutinated rabbit erythrocytes showing stability even after 1 h of exposure to a different pH values (optimal between pH 6.0 and 8.0) but was inhibited after incubation with d-mannose and d-glucose. The pure protein possessed a molecular weight of 25 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis and 25,410Da by mass spectrometry. The results analyzed by the software SELCON 3 indicate that β-sheet secondary structures are predominant in DLL (approximately 40.2% antiparallel β-sheet, 4.6% parallel β-sheet, 7.2% α-helices, 17.3% turns, and 28.7% unordered structures). Mechanical activity of isolated aorta from rat measured by cumulative concentration curves of DLL, performed at the contraction plateau induced by phenylephrine in either endothelium-intact or denuded aorta. DLL (IC50 = 34.12 ± 3.46 µg/ml) relaxed precontracted endothelized aortic rings by 34.61 ± 9.06%, 55.19 ± 11.9%, and 81.33 ± 14.35%, respectively, at 10 µg/ml (initial concentration), 30 µg/ml, and 100 µg/ml (maximum effect). All effects occurred via interaction with lectin domains and participation of nitric oxide. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]