The conjecture that helicity (or knottedness) is a fundamental conserved quantity has a rich history in fluid mechanics, but the nature of this conservation in the presence of dissipation has proven difficult to resolve. Making use of recent advances, we create vortex knots and links in viscous fluids and simulated superfluids and track their geometry through topology-changing reconnections. We find that the reassociation of vortex lines through a reconnection enables the transfer of helicity from links and knots to helical coils. This process is remarkably efficient, owing to the antiparallel orientation spontaneously adopted by the reconnecting vortices. Using a new method for quantifying the spatial helicity spectrum, we find that the reconnection process can be viewed as transferring helicity between scales, rather than dissipating it. We also infer the presence of geometric deformations that convert helical coils into even smaller scale twist, where it may ultimately be dissipated. Our results suggest that helicity conservation plays an important role in fluids and related fields, even in the presence of dissipation.
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http://dx.doi.org/10.1073/pnas.1407232111 | DOI Listing |
Front Mol Biosci
January 2025
Center for Biomolecular and Cellular Structure, Institute for Basic Science, Daejeon, Republic of Korea.
Huntington's disease (HD) is primarily caused by the aberrant aggregation of the N-terminal exon 1 fragment of mutant huntingtin protein (mHttex1) with expanded polyglutamine (polyQ) repeats in neurons. The first 17 amino acids of the N-terminus of Httex1 (N17 domain) immediately preceding the polyQ repeat domain are evolutionarily conserved across vertebrates and play multifaceted roles in the pathogenesis of HD. Due to its amphipathic helical properties, the N17 domain, both alone and when membrane-associated, promotes mHttEx1 aggregation.
View Article and Find Full Text PDFNat Mater
January 2025
Department of Physics, Harvard University, Cambridge, MA, USA.
Atomically thin van der Waals (vdW) films provide a material platform for the epitaxial growth of quantum heterostructures. However, unlike the remote epitaxial growth of three-dimensional bulk crystals, the growth of two-dimensional material heterostructures across atomic layers has been limited due to the weak vdW interaction. Here we report the double-sided epitaxy of vdW layered materials through atomic membranes.
View Article and Find Full Text PDFBiochimie
January 2025
School of Chemistry and Biological Engineering, University of Science and Technology Beijing, Beijing, 100083, China. Electronic address:
Microorganisms play a crucial role in the degradation of microcystins (MCs), with most MC-degrading bacteria utilizing the mlr gene cluster (mlrABCD) mechanism. While previous studies have advanced our understanding of the structure, function, and degradation mechanisms of MlrA, MlrB, and MlrC, research on MlrD remains limited. Consequently, the molecular structure and specific catalytic processes of MlrD are still unclear.
View Article and Find Full Text PDFCRISPR-Cas12a is widely used for genome editing and biomarker detection since it can create targeted double-stranded DNA breaks and promote non-specific DNA cleavage after identifying specific DNA. To mitigate the off-target DNA cleavage of Cas12a, we previously developed a Cas12a variant (FnoCas12a ) by introducing double proline substitutions (K969P/D970P) in a conserved helix called the bridge helix (BH). In this work, we used cryogenic electron microscopy (cryoEM) to understand the molecular mechanisms of BH- mediated activation of Cas12a.
View Article and Find Full Text PDFJ Mol Biol
January 2025
Instituto de Investigaciones Biomédicas Sols-Morreale CSIC-UAM, 28029 Madrid, Spain. Electronic address:
A key step in autophagy is the conjugation by the E3-like Atg12-Atg5-Atg16 complex of the ubiquitin-like protein Atg8 to phosphatidylethanolamine on the autophagosomal membrane, a process known as lipidation. Previous work in yeast showed that recruitment of the E3-like complex to the preautophagosomal structure is mediated by the interaction of Atg16 with the phosphatidylinositol 3-phosphate-binding protein Atg21, and by the association of Atg12 with the scaffold protein of the Atg1 kinase complex, Atg17. Here, we conducted a reverse two-hybrid screen to identify residues in Atg17 and Atg12 critical for Atg17-Atg12 binding, and used these data to generate a docking model of Atg12-Atg5-Atg16 with the Atg17 complex.
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