Ruffling is Essential for Staphylococcus aureus IsdG-catalyzed Degradation of Heme to Staphylobilin

Non-canonical heme oxygenases are enzymes that degrade heme to non-biliverdin products within bacterial heme iron acquisition pathways. These enzymes all contain a conserved second-sphere Trp residue that is essential for enzymatic turnover. Previous studies have revealed several important roles for the conserved second-sphere Trp in Staphylococcus aureus IsdG, S. aureus IsdI, and Mycobacterium tuberculosis MhuD. However, a general model for the geometric, electronic, and functional role of the second-sphere Trp had not been deduced prior to this work. Here, UV/Vis absorption (Abs) and circular dichroism (CD) spectroscopies were employed to show that the W67F variant of IsdG perturbs the heme substrate conformation without altering the protein secondary structure. In general, it can now be stated that a dynamic equilibrium between “planar” and “ruffled” substrate conformations exists within non-canonical heme oxygenases, and that the second-sphere Trp favors population of the “ruffled” substrate conformation. 1H nuclear magnetic resonance and magnetic CD spectroscopies were used to characterize the electronic structures of IsdG and IsdI variants with different substrate conformational distributions. These data revealed that the “ruffled” substrate conformation promotes partial porphyrin-to-iron electron transfer, which makes the meso carbons of the porphyrin ring susceptible to radical attack. Finally, UV/Vis Abs spectroscopy was utilized to quantify the enzymatic rates, and electrospray ionization mass spectrometry was used to identify the product distributions, for variants of IsdG with altered substrate conformational distributions. In general, the rate of heme oxygenation by non-canonical heme oxygenases depends upon the population of the “ruffled” substrate conformation. Also, the production of staphylobilin or mycobilin by these enzymes is correlated with the population of the “ruffled” substrate conformation, since variants that favor population of the “planar” substrate conformation yield significant amounts of biliverdin. These data can be understood within the framework of a concerted rearrangement mechanism for the monooxygenation of heme to meso-hydroxyheme by non-canonical heme oxygenases. However, the mechanisms of IsdG/IsdI and MhuD must diverge following this intermediate in order to generate distinct staphylobilin and mycobilin products, respectively.

A printed lens in antenna’s aperture to improve the performance of UWB-radar system

Abstractwe present a printed lens for radar applications. The structure of the presented lens consists of an array of modified micro-strip lines, which is positioned in the antenna’s aperture on the same planar substrate. Simulations show that the gain and directivity increase with the proposed lens in a wide band frequency band. The proposed design is insensitive to rotation of the antenna. This paper focuses on real industrial applications and problems. Further, we show that the lens can be used to improve the object detection ability of an ultrawide band radar system, which is used in industrial applications such as non-destructive monitoring of built-structures and for use in the renovation process. The signal to noise ratio is improved. Furthermore, we show how the microwave lens can also be used to reduce the clutter in applications where the complex refractive index of objects is determined. Further, different simulated results (for different cases) are compared, presented and concluded.

Patterns formed in a thin film with spatially homogeneous and non-homogeneous Derjaguin disjoining pressure

We consider patterns formed in a two-dimensional thin film on a planar substrate with a Derjaguin disjoining pressure and periodic wettability stripes. We rigorously clarify some of the results obtained numerically by Honisch et al. [Langmuir 31: 10618–10631, 2015] and embed them in the general theory of thin-film equations. For the case of constant wettability, we elucidate the change in the global structure of branches of steady-state solutions as the average film thickness and the surface tension are varied. Specifically we find, by using methods of local bifurcation theory and the continuation software package AUTO, both nucleation and metastable regimes. We discuss admissible forms of spatially non-homogeneous disjoining pressure, arguing for a form that differs from the one used by Honisch et al., and study the dependence of the steady-state solutions on the wettability contrast in that case.

Leaky Wave Array in Full Planar Substrate with EBG-Based Wave Guiding Channel

A new type of wave guiding structure is proposed is this paper. The guiding channel is developed on the full planar dielectric substrate and aligned with electromagnetic bandgap (EBG) units. Since the bandgap of these mushroom-like units is calculated with a coverage of the channel working band, these units are of great importance on ensuring the transmission efficiency and eliminating the coupling effect between channels. Then, this wave guiding structure is extended to the design of a six-element leaky wave antenna array with a complete size of 25.6 mm × 80.6 mm, which is working at Ku band from 12.0 GHz to 12.8 GHz and achieving a bandwidth of about 0.8 GHz, a gain of 11.36 dBi, and an efficiency of ca. 86.7% at 12.0 GHz. Within the working frequency band, this antenna topology achieves a frequency-dependent beam scanning in the forward directions, and it offers a potential for radar application on road speed detecting with low costs.

A Dynamic Substrate is Required for MhuD-catalyzed Degradation of Heme to Mycobilin

The non-canoncial heme oxygenase MhuD from <i>Mycobacterium tuberculosis</i> binds a heme substrate that adopts a dynamic equilibrium between planar and out-of-plane ruffled conformations. MhuD degrades this substrate to an unusual mycobilin product via successive monooxygenation and dioxygenation reactions. This article establishes a causal relationship between heme substrate dynamics and MhuD-catalyzed heme degradation resulting in a refined enzymatic mechanism. UV/Vis absorption (Abs) and electrospray ionization mass spectrometry (ESI-MS) data demonstrated that a second-sphere substitution favoring population of the ruffled heme conformation changed the rate-limiting step of the reaction resulting in a measurable build-up of the monooxygenated meso-hydroxyheme intermediate. In addition, UV/Vis Abs and ESI-MS data for a second-sphere variant that favored the planar substrate conformation showed that this change altered the enzymatic mechanism resulting in an alpha-biliverdin product. Single-turnover kinetic analyses for three MhuD variants revealed that the rate of heme monooxygenation depends upon the population of the ruffled substrate conformation. These kinetic analyses also revealed that the rate of meso-hydroxyheme dioxygenation by MhuD depends upon the population of the planar substrate conformation. Thus, the ruffled haem conformation supports rapid heme monooxygenation by MhuD, but further oxygenation to the mycobilin product is inhibited. In contrast, the planar substrate conformation exhibits altered heme monooxygenation regiospecificity followed by rapid oxygenation of meso-hydroxyheme. Altogether, these data yielded a refined enzymatic mechanism for MhuD where access to both substrate conformations is needed for rapid incorporation of three oxygen atoms into heme yielding mycobilin.<br>

A Dynamic Substrate is Required for MhuD-catalyzed Degradation of Heme to Mycobilin

The non-canoncial heme oxygenase MhuD from <i>Mycobacterium tuberculosis</i> binds a heme substrate that adopts a dynamic equilibrium between planar and out-of-plane ruffled conformations. MhuD degrades this substrate to an unusual mycobilin product via successive monooxygenation and dioxygenation reactions. This article establishes a causal relationship between heme substrate dynamics and MhuD-catalyzed heme degradation resulting in a refined enzymatic mechanism. UV/Vis absorption (Abs) and electrospray ionization mass spectrometry (ESI-MS) data demonstrated that a second-sphere substitution favoring population of the ruffled heme conformation changed the rate-limiting step of the reaction resulting in a measurable build-up of the monooxygenated meso-hydroxyheme intermediate. In addition, UV/Vis Abs and ESI-MS data for a second-sphere variant that favored the planar substrate conformation showed that this change altered the enzymatic mechanism resulting in an alpha-biliverdin product. Single-turnover kinetic analyses for three MhuD variants revealed that the rate of heme monooxygenation depends upon the population of the ruffled substrate conformation. These kinetic analyses also revealed that the rate of meso-hydroxyheme dioxygenation by MhuD depends upon the population of the planar substrate conformation. Thus, the ruffled haem conformation supports rapid heme monooxygenation by MhuD, but further oxygenation to the mycobilin product is inhibited. In contrast, the planar substrate conformation exhibits altered heme monooxygenation regiospecificity followed by rapid oxygenation of meso-hydroxyheme. Altogether, these data yielded a refined enzymatic mechanism for MhuD where access to both substrate conformations is needed for rapid incorporation of three oxygen atoms into heme yielding mycobilin.<br>

Hysteresis in spreading and retraction of liquid droplets on parallel fiber rails

Wetting and spreading of liquids on fibers occurs in many natural and artificial processes. Unlike on a planar substrate, a droplet attached to one or more fibers can assume several...