Non-canonical shedding of TNFα by SPPL2a is determined by the conformational flexibility of its transmembrane helix

Ectodomain (EC) shedding defines the proteolytic removal of a membrane protein EC and acts as an important molecular switch in signaling and other cellular processes. Using tumor necrosis factor (TNF)α as a model substrate, we identify a non-canonical shedding activity of SPPL2a, an intramembrane cleaving aspartyl protease of the GxGD type. Proline insertions in the TNFα transmembrane (TM) helix strongly increased SPPL2a non-canonical shedding, while leucine mutations decreased this cleavage. Using biophysical and structural analysis, as well as molecular dynamic simulations, we identified a flexible region in the center of the TNFα wildtype TM domain, which plays an important role in the processing of TNFα by SPPL2a. This study combines molecular biology, biochemistry, and biophysics to provide insights into the dynamic architecture of a substrate\u27s TM helix and its impact on non-canonical shedding. Thus, these data will provide the basis to identify further physiological substrates of non-canonical shedding in the future

Non-canonical Shedding of TNFα by SPPL2a Is Determined by the Conformational Flexibility of Its Transmembrane Helix

Ectodomain (EC) shedding defines the proteolytic removal of a membrane protein EC and acts as an important molecular switch in signaling and other cellular processes. Using tumor necrosis factor (TNF)α as a model substrate, we identify a non-canonical shedding activity of SPPL2a, an intramembrane cleaving aspartyl protease of the GxGD type. Proline insertions in the TNFα transmembrane (TM) helix strongly increased SPPL2a non-canonical shedding, while leucine mutations decreased this cleavage. Using biophysical and structural analysis, as well as molecular dynamic simulations, we identified a flexible region in the center of the TNFα wildtype TM domain, which plays an important role in the processing of TNFα by SPPL2a. This study combines molecular biology, biochemistry, and biophysics to provide insights into the dynamic architecture of a substrate\u27s TM helix and its impact on non-canonical shedding. Thus, these data will provide the basis to identify further physiological substrates of non-canonical shedding in the future

Investigations into the structure of La3Ni2−xFexO7±δ

The room-temperature (RT) 57Fe Mössbauer spectra of the La3Ni2−xFexO7±δ oxide solid solutions of Ruddlesden-Popper-type (x = 0.05, 0.10) reveal two doublets for Fe3+ ions in octahedral coordination by oxygen. The existence of two inequivalent sites for Fe at RT is at variance with the space groups Fmmm and Cmcm (Amam) which have been reported for La3Ni2O7±δ. This unexpected finding is discussed in connection with Patterson analyses and Rietveld refinements of powder XRD data for x = 0, 0.05, and 0.10. Alternative structural models have been proposed which can explain the spectroscopic findings and which are compatible with the results from X-ray diffraction

GRB 040403: a faint X-ray rich Gamma-ray Burst discovered by INTEGRAL

GRB 040403 is one of the faintest gamma-ray bursts for which a rapid and accurate localization has been obtained. Here we report on the gamma-ray properties of this burst, based on observations with the IBIS instrument aboard INTEGRAL, and the results of searches for its optical afterglow. The steep spectrum (power law photon index =1.9 in the 20–200 keV range) implies that GRB 040403 is most likely an X-ray rich burst. Our optical limit of R \u3e24.2 at 16.5 h after the burst, indicates a rather faint afterglow, similar to those seen in other relatively soft and faint bursts