Using a zebrafish model of hepatoerythropoietic porphyria (HEP), we identify a previously unknown mechanism underlying heme-mediated regulation of exocrine zymogens. Zebrafish bach1b, nrf2a and mafK are all expressed in the zebrafish exocrine pancreas. Overexpression of bach1b or knockdown of nrf2a result in the downregulation of the expression of the exocrine zymogens, whereas overexpression of nrf2a or knockdown of bach1b cause their upregulation. In vitro luciferase assays demonstrate that heme activates the zymogens in a dosage-dependent manner and that the zymogen promoter activities require the integral Maf recognition element (MARE) motif. The Bach1b-MafK heterodimer represses the zymogen promoters, whereas the Nrf2a-MafK heterodimer activates them. Furthermore, chromatin immunoprecipitation (ChIP) assays show that MafK binds to the MARE sites in the 5′ regulatory regions of the zymogens. Taken together, these data indicate that heme stimulates the exchange of Bach1b for Nrf2a at MafK-occupied MARE sites and that, particularly in heme-deficient porphyria, the repressive Bach1b-MafK heterodimer dominates, which can be exchanged for the activating Nrf2a-MafK heterodimer upon treatment with hemin. These results provide novel insights into the regulation of exocrine function, as well as the pathogenesis of porphyria, and should be useful for designing new therapies for both types of disease.
Natural proteins display organized hierarchical structures and tailored functionalities that cannot be achieved by synthetic approaches, highlighting the increased interest in developing protein‐based materials. Protein self‐assembly allows fabricating sophisticated supramolecular structures from relatively simple building blocks, a strategy naturally employed by amyloid proteins and intrinsically disordered proteins. However, the design of self‐assembled bioinspired materials with multi functionalities is still challenging. Inspired by the natural self‐assembly proteins (such as mussel foot proteins and amyloid proteins), a temperature‐inducible engineering programable hydrogel‐like amyloid nanostructure is developed by using a genetically modular fusion approach. The resulting hydrogel‐like assemblies display outstanding adhesive capacity, high stability, and broad substrate universality. The employed SpyCatcher/SpyTag system allows modifying the hydrogel‐like assemblies with any functional proteins of interest. Owing to their strong adhesive capacity and functional flexibility, such amyloid fibril‐based hydrogel shows advantages in the immobilization of diverse enzymes for highly efficient biocatalysis, fabrication of multi‐layered functional coatings, and construction of functionalized 3D scaffold for cell culture. Overall, a modular and straightforward approach is established to obtain a genetically programable nanostructure platform. The novel hydrogel‐like assemblies described here may be potentially applied to but not limited to synthetic biology, surface/interface engineering, and tissue engineering.
To facilitate its survival, replication, and dissemination, the intracellular pathogen Legionella pneumophila relies on its unique Type IVB secretion system (T4SS) to deliver over 330 effectors to hijack host cell pathways in a spatiotemporal manner. The underlying mechanisms of the effectors and their host targets are largely unexplored due to their little sequence identity to known proteins and functional redundancy. The T4SS effector SidN (Lpg1083) is secreted into host cells during the late infection period. However, to the best of our knowledge, the molecular characterization of SidN has not been previously studied. Herein, we identified SidN as a nuclear envelope-localized effector. Its structure adopts a novel fold and the N-terminal domain is crucial for its specific subcellular localization. Furthermore, we found that SidN is transported by the eukaryotic karyopherin Importin-13 into the nucleus, where it attaches to the N-terminal region of Lamin-B2 to interfere with the integrity of the nuclear envelope, causing nuclear membrane disruption and eventually cell death. Our work provides new insights into the structure and function of an L. pneumophila effector protein, and suggests a potential strategy that the pathogen utilizes to promote cell death and then benefit bacterial escape from the host for secondary infection.
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