[3dem] Announcing the One World Cryo-EM Algorithms Seminars

[Roy Lederman]

Dear Friends,


We would like to invite you to One World Cryo-EM, an online seminar series
about algorithms and mathematics in cryo-EM. We hope that these seminars
will allow our community to catch up and welcome new members.


First talk:

*Cryo-EM and Helical Polymers: A Natural Affinity. *

*Edward H Egelman. *

*September 23rd at 8am PT / 11am ET / 4pm BST / 5pm CEST / 11pm China, via
Zoom*. Join us 10 minutes early for informal tea time and to check that
everything works.


*Please register early*:
https://urldefense.com/v3/__https://yale.zoom.us/meeting/register/tJApcu6grD4iGdFaQsDVdpJEaGD1oE-3VOjB__;!!Mih3wA!Tpypsbm9Jhum8Y9PdlhGu5QaxuU0znb-oUNm73O7NQrpnVr_Di7g23WCdqgLmn02eA$ 

Unfortunately, we have to approve your free registration manually. Please
register early using your institution or company email and with information
that would help us verify that you are a human.


Future seminars, every other Wednesday, will include additional networking
and lightning talk opportunities.


*See you there!*

   Joakim Andén

   Dorit Hanein

   Roy R. Lederman

   Steven J. Ludtke


For updates:

*Visit: https://urldefense.com/v3/__https://cryoem.world/__;!!Mih3wA!Tpypsbm9Jhum8Y9PdlhGu5QaxuU0znb-oUNm73O7NQrpnVr_Di7g23WCdqi8Pjk3IA$  <https://urldefense.com/v3/__https://cryoem.world/__;!!Mih3wA!Tpypsbm9Jhum8Y9PdlhGu5QaxuU0znb-oUNm73O7NQrpnVr_Di7g23WCdqi8Pjk3IA$ >*

*Follow: @OWCryoEM*

*Join our mailing list (read-only announcements):
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----------------------------



*Cryo-EM and Helical Polymers: A Natural Affinity*

*Edward H Egelman*, Professor, Biochemistry and Molecular Genetics,
University of Virginia

Date and time: 9/23/2020 Wednesday, at 8am PT / 11am ET/ 4pm BST / 5pm CEST
/ 11pm China

Please register in advance:
https://urldefense.com/v3/__https://yale.zoom.us/meeting/register/tJApcu6grD4iGdFaQsDVdpJEaGD1oE-3VOjB__;!!Mih3wA!Tpypsbm9Jhum8Y9PdlhGu5QaxuU0znb-oUNm73O7NQrpnVr_Di7g23WCdqgLmn02eA$ 


It was over fifty years ago that the first 3D reconstruction from electron
microscopy was published (DeRosier and Klug, 1968), and this happened to be
a helical phage tail. It was no accident that this was a helical specimen,
and not just because helical polymers are so abundant in biology. From one
point of view helical objects are the simplest to reconstruct: a single
image of a helical filament may provide all of the information needed for a
3D reconstruction. Fourier-Bessel methods of reconstruction dominated the
field for the next 30 years, but now real-space approaches have become the
standard. With the advent of direct-electron detectors, reaching a
near-atomic resolution for helical polymers has become the standard, rather
than the exception. However, problems in determining the correct helical
symmetry can persist even when one reaches a resolution of ~ 5 Å. I will
discuss how the best approach to determining helical symmetry involves an
averaged power spectrum from the images, and explain why the power spectrum
of an averaged image (such as using Class2D) is not the same as the
averaged power spectrum. In addition, the highly anisotropic environment
present in thin films prior to vitrification, the compressional forces
associated with these thin films, and fluid flow with associated shear, can
all impact the structure of the filaments being examined. I will discuss
these problems and potential solutions while giving an overview of some of
our own efforts involving everything from viruses infecting hosts living in
nearly boiling acid to microbial nanowires, with stops along the way at
bacterial and archaeal flagellar filaments and bacterial and archaeal pili.
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