Molecular & Cell Biophysics Sunday Talks

Rainy Rainy Day in Baltimore

I will highlight two talks from the 10 or so I saw today but it was also really great to hear a presentation from Steven Chu, the Secretary of Energy who mostly talked about his science (he is a Nobel laureate physicist) but also talked about energy and the need to fund basic research.

Here are my favorite talks (be sure to check the bottom one):

11:15 PM  Engineering Cells to Grow Dielectrical Interfaces with Materials ~ Caroline M. Ajo-Franklin, Lawrence Berkeley Lab

How can we instruct living cells (one feature is that they self heal rather than just break such as if you throw your computer on floor-uh oh) to construct electrical interfaces with nonliving systems (feature is that they exhibit rapid communication such as cell phones rather than carrier pigeons).  Realize that living cells can do sensing work and calculations  BUT, they are so mechanically different:  living cells are disorganized, soft, dielectric constant, and they are intrinsically insulators; two insulating barriers (gram negative bacteria).  Can we recode genetics to define electronic path for electrons to flow?  Turn to living organisms – they have worked on problems for 4 x 10⁹ years, turns out that some cells, s. oneidensis, transfer electrons to Fe⁺³ to Fe⁺² extracellular electron transfer pathway, soluble in periplasm or solid in extracellular space.  Transmembrane proteins MtrC and MtrB can reduce Fe⁺³ to Fe⁺² multiheme proteinsElectronic coli, e- coli to get electron transport, but these genes into e.coli to get e- coli.  Get lots of Fe⁺² productionMost active character is the MtrA for soluble Fe⁺³ but Mtr trimeric CAB reduces SOLID Fe₂O₃, but 10x worse than s. oneidensis.  We can do better, we need to shuttle electrons from lactate to quinone and this might be down regulated, how to eliminate bottlenecks?  Selecting cells with e-coli survives much longer, look for directed evolution screen.

12: 15 AM Structure of the Torque Ring of the Bacterial Flagellar Motor and Molecular basis for Rotational Switching  - Lawrence Lee  ~ Australia

E. coli motility (Turner J. Bacteriology 2000 182)

runs (flagella all together - lasts several secs) and tumbles (tenths of seconds).  11 mega Daltons, 13 diff proteins, 100,000 rpm and can reverse in milliseconds.  CCW all filaments combine for run. CW for some filaments, whole system switches to tumble.  Chemotaxis in head of E. coli generates Che-Y.  Switch complex: FliG (flygee), FliM, FliN.  X-ray structure exists for FliG – conformational change, generates rotations torque.  N, middle, C terminal.  Mutations torque generating helix, torque generating helix, electrostatic chage, Arg+ 90/Glu- 98 interact with MotA counter ion pairs.  Closed conformation; long middle helix and middle helix,  CCW (run) closed complex of FliG, CW (tumble) switch to open conformation.  FliM, two independent binding sites on FliG  -- ARM repeats hydrophobic VLI tripeptides to tandem ARM right handed alpha helices, stacking of tandem ARM repeats, conserved, creates surface for FliM binding.  Mechanism for multimerization of FliG multimers.

This guy had THE most amazing movies of these transitions, but talked so fast it was hard to follow the details.  Check out Lee's website.