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1. Combing a double helix

   https://doi.org/10.1039/d1sm01533h  

   Plumb-Reyes, Thomas B.; Charles, Nicholas; Mahadevan, L. (April 2022, Soft Matter)

   Combing hair involves brushing away the topological tangles in a collective curl, defined as a bundle of interacting elastic filaments. Using a combination of experiment and computation, we study this problem that naturally links topology, geometry and mechanics. Observations show that the dominant interactions in hair are those of a two-body nature, corresponding to a braided homochiral double helix. This minimal model allows us to study the detangling of an elastic double helix driven by a single stiff tine that moves along it and leaves two untangled filaments in its wake. Our results quantify how the mechanics of detangling correlates with the dynamics of a topological quantity, the link density, that propagates ahead of the tine and flows out the free end as a link current. This in turn provides a measure of the maximum characteristic length of a single combing stroke in the many-body problem on a head of hair, producing an optimal combing strategy that balances trade-offs between comfort, efficiency and speed of combing in hair curls of varying geometrical and topological complexity. 

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2. A thermophilic phage uses a small terminase protein with a fixed helix–turn–helix geometry

   https://doi.org/10.1074/jbc.RA119.012224  

   Hayes, Janelle A.; Hilbert, Brendan J.; Gaubitz, Christl; Stone, Nicholas P.; Kelch, Brian A. (March 2020, Journal of Biological Chemistry)

   Tailed bacteriophages use a DNA-packaging motor to encapsulate their genome during viral particle assembly. The small terminase (TerS) component of this DNA-packaging machinery acts as a molecular matchmaker that recognizes both the viral genome and the main motor component, the large terminase (TerL). However, how TerS binds DNA and the TerL protein remains unclear. Here we identified gp83 of the thermophilic bacteriophage P74-26 as the TerS protein. We found that TerS P76-26 oligomerizes into a nonamer that binds DNA, stimulates TerL ATPase activity, and inhibits TerL nuclease activity. A cryo-EM structure of TerS P76-26 revealed that it forms a ring with a wide central pore and radially arrayed helix–turn–helix domains. The structure further showed that these helix–turn–helix domains, which are thought to bind DNA by wrapping the double helix around the ring, are rigidly held in an orientation distinct from that seen in other TerS proteins. This rigid arrangement of the putative DNA-binding domain imposed strong constraints on how TerS P76-26 can bind DNA. Finally, the TerS P76-26 structure lacked the conserved C-terminal β-barrel domain used by other TerS proteins for binding TerL. This suggests that a well-ordered C-terminal β-barrel domain is not required for TerS P76-26 to carry out its matchmaking function. Our work highlights a thermophilic system for studying the role of small terminase proteins in viral maturation and presents the structure of TerS P76-26 , revealing key differences between this thermophilic phage and its mesophilic counterparts. 

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3. When Is a Helix Stable?

   https://doi.org/10.1103/PhysRevLett.125.088001  

   Borum, Andy; Bretl, Timothy (August 2020, Physical Review Letters)

   null (Ed.)
4. DNA double helix, a tiny electromotor

   https://doi.org/10.1038/s41565-022-01285-z  

   Maffeo, Christopher; Quednau, Lauren; Wilson, James; Aksimentiev, Aleksei (December 2022, Nature Nanotechnology)

   Flowing fluid past chiral objects has been used for centuries to power rotary motion in man-made machines. By contrast, rotary motion in nanoscale biological or chemical systems is produced by biasing Brownian motion through cyclic chemical reactions. Here we show that a chiral biological molecule, a DNA or RNA duplex rotates unidirectionally at billions of revolutions per minute when an electric field is applied along the duplex, with the rotation direction being determined by the chirality of the duplex. The rotation is found to be powered by the drag force of the electro-osmotic flow, realizing the operating principle of a macroscopic turbine at the nanoscale. The resulting torques are sufficient to power rotation of nanoscale beads and rods, offering an engineering principle for constructing nanoscale systems powered by electric field. 

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5. Covalent Capture of a Heterotrimeric Collagen Helix

   https://doi.org/10.1021/acs.orglett.9b01771  

   Li, I-Che; Hulgan, Sarah A.; Walker, Douglas R.; Farndale, Richard W.; Hartgerink, Jeffrey D.; Jalan, Abhishek A. (July 2019, Organic Letters)