More Like this

1. Helix formation and stability in membranes

   https://doi.org/10.1016/j.bbamem.2018.02.010  

   McKay, Matthew J.; Afrose, Fahmida; Koeppe, Roger E.; Greathouse, Denise V. (October 2018, Biochimica et Biophysica Acta (BBA) - Biomembranes)
2. 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. 

   more » « less
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. 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. 

   more » « less
5. The Ribbon-Helix-Helix Domain Protein CdrS Regulates the Tubulin Homolog ftsZ2 To Control Cell Division in Archaea

   https://doi.org/10.1128/mBio.01007-20  

   Darnell, Cynthia L.; Zheng, Jenny; Wilson, Sean; Bertoli, Ryan M.; Bisson-Filho, Alexandre W.; Garner, Ethan C.; Schmid, Amy K. (August 2020, mBio)

   Søgaard-Andersen, Lotte (Ed.)

   ABSTRACT Precise control of the cell cycle is central to the physiology of all cells. In prior work we demonstrated that archaeal cells maintain a constant size; however, the regulatory mechanisms underlying the cell cycle remain unexplored in this domain of life. Here, we use genetics, functional genomics, and quantitative imaging to identify and characterize the novel CdrSL gene regulatory network in a model species of archaea. We demonstrate the central role of these ribbon-helix-helix family transcription factors in the regulation of cell division through specific transcriptional control of the gene encoding FtsZ2, a putative tubulin homolog. Using time-lapse fluorescence microscopy in live cells cultivated in microfluidics devices, we further demonstrate that FtsZ2 is required for cell division but not elongation. The cdrS-ftsZ2 locus is highly conserved throughout the archaeal domain, and the central function of CdrS in regulating cell division is conserved across hypersaline adapted archaea. We propose that the CdrSL-FtsZ2 transcriptional network coordinates cell division timing with cell growth in archaea. IMPORTANCE Healthy cell growth and division are critical for individual organism survival and species long-term viability. However, it remains unknown how cells of the domain Archaea maintain a healthy cell cycle. Understanding the archaeal cell cycle is of paramount evolutionary importance given that an archaeal cell was the host of the endosymbiotic event that gave rise to eukaryotes. Here, we identify and characterize novel molecular players needed for regulating cell division in archaea. These molecules dictate the timing of cell septation but are dispensable for growth between divisions. Timing is accomplished through transcriptional control of the cell division ring. Our results shed light on mechanisms underlying the archaeal cell cycle, which has thus far remained elusive. 

   more » « less