Analysis of Chain Branch of Polyolefins by a New Proton NMR Approach

The crystallinity of polyethylene, which significantly affects the properties of the polymer, is quite sensitive to the concentration of its branches. Thus, it is necessary to estimate branch concentration with reasonable accuracy. Currently, ¹³C NMR and gel permeation chromatography–Fourier transform infrared spectroscopy are widely-used analysis methods for the analysis of branch concentration. Despite several advantages, these methods sometimes have limitations. For instance, the preparation of samples for ¹³C- NMR is tedious because high-concentration samples are required and the time for analysis is greater than 12 h. To more efficiently estimate the branch concentration of polyethylene, we developed a new high-field ¹H NMR method with an improved peak resolution by employing (1) homonuclear decoupling and (2) 2D heteronuclear correlation. The new method was observed to significantly reduce the experimental time to ∼30 min; furthermore, sample preparation was relatively simple because the method did not require high-concentration samples

The 1:2 complex between RavZ and LC3 reveals a mechanism for deconjugation of LC3 on the phagophore membrane

<p>Hosts utilize macroautophagy/autophagy to clear invading bacteria; however, bacteria have also developed a specific mechanism to survive by manipulating the host cell autophagy mechanism. One pathogen, <i>Legionella pneumophila</i>, can hinder host cell autophagy by using the specific effector protein RavZ that cleaves phosphatidylethanolamine-conjugated LC3 on the phagophore membrane. However, the detailed molecular mechanisms associated with the function of RavZ have hitherto remained unclear. Here, we report on the biochemical characteristics of the RavZ-LC3 interaction, the solution structure of the 1:2 complex between RavZ and LC3, and crystal structures of RavZ showing different conformations of the active site loop without LC3. Based on our biochemical, structural, and cell-based analyses of RavZ and LC3, both distant flexible N- and C-terminal regions containing LC3-interacting region (LIR) motifs are important for substrate recognition. These results suggest a novel mechanism of RavZ action on the phagophore membrane and lay the groundwork for understanding how bacterial pathogens can survive autophagy.</p