The Physics department colloquia are usually on Friday afternoons at 3 pm in Room 135. Coffee and cookies are served at 2:45 pm in the same room. Anyone is welcome.

Mapping Dynamic Nature of Molecular Machines that constitute Life
Dr. Peter Schwander, Senior Scientist, UW-Milwaukee (Tampa, FL)

Fighting disease and maintaining life requires a good understanding of the machinery inside living cells. These biological molecular machines go permanently through many conformational states, and each state is structurally only slightly different from the previous one. Single-particle methods take individual snapshots of molecules, one at a time. Single-particle methods thus avoid averaging over states and are therefore ideally suited to study conformations. When successful, this allows compiling 3D movies of molecular machines at work.

A novel analytic approach, based on manifold embedding, allows model-free, quantitative analysis of the degrees of freedom and the energy landscape underlying continuous conformational changes from single-particle methods. This approach has been successfully applied to snapshots of the eukaryotic ribosome taken with a cryogenetic electron microscope (cryoEM). The results constitute the first direct evidence of the intersubunit rotation in three dimensions, and suggest the ribosome to act like a Brownian ratchet.

Similar to cryoEM, the emerging X-ray Free Energy Laser (XFEL) allows taking snapshots from single molecules before the intense beam destroys them, XFEL thus provides a new source of single-particle snapshots to study conformations and will complement the more established cryoEM in the near future.