The YtfE protein catalyzes the reduction of NO to N2O, protecting iron–sulfur clusters from nitrosylation. The structure of YtfE has a two-domain architecture, with a diiron-containing C-terminal domain linked to an N-terminal domain, in which the function of the latter is enigmatic. Here, by using electron spin resonance (ESR) spectroscopy, we show that YtfE exists in two conformational states, one of which has not been reported. Under high osmotic stress, YtfE adopts a homogeneous conformation (C state) similar to the known crystal structure. In a regular buffer, the N-terminal domain switches between the C state and a previously unidentified conformation (C′ state), the latter of which has more space at the domain interface to allow the trafficking of NO molecules and thus is proposed to be a functionally active state. The conformational switch between the C and C′ states is pivotal for facilitating NO access to the diiron core.
Prion diseases are transmissible fatal neurodegenerative disorders spreading between humans and other mammals. The pathogenic agent, prion, is a protease-resistant, β-sheet-rich protein aggregate, converted from a membrane protein called PrP C . PrP Sc is the misfolded form of PrP C and undergoes selfpropagation to form the infectious amyloids. Since the key hallmark of prion disease is amyloid formation, identifying and studying which segments are involved in the amyloid core can provide molecular details about prion diseases. It has been known that the prion protein could also form non-infectious fibrils in the presence of denaturants. In this study, we employed a combination of site-directed nitroxide spin-labeling, fibril seeding, and electron spin resonance (ESR) spectroscopy to identify the structure of the in vitro-prepared full-length mouse prion fibrils. It is shown that in the in vitro amyloidogenesis, the formation of the amyloid core is linked to an α-to-β structural transformation involving the segment 160-224, which contains strand 2, helix 2, and helix 3. This method is particularly suitable for examining the hetero-seeded amyloid fibril structure, as the unlabeled seeds are invisible by ESR spectroscopy.It can be applied to study the structures of different strains of infectious prions or other amyloid fibrils in the future.
We have successfully demonstrated the fabrication of piezoelectric PDMS films utilizing casting, stacking, and micro plasma discharge processes. To realize electromechanical sensitivity, PDMS structures with micrometer-sized cells are implanted with positive and negative charges on the opposite internal surfaces of each cell, which behaves just like a dipole. In the prototype demonstration, multilayer PDMS films with inner cells of 50×50×50 μm 3 are fabricated and charged under electric fields up to 40 MV/m. The resulting cellular PDMS films show an elastic modulus of at least 12% lower than solid ones and a piezoelectric coefficient (d 33 ) up to 182 pC/N, which is about 10 times higher than that of common piezoelectric polymers (e.g., PVDF). As such, the demonstrated piezoelectric PDMS films could serve as soft and sensitive electromechanical transducers, which are desired for a variety of sensor and energy har-vesting applications.
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