Biophysical Society 67th Annual Meeting Program Guide

Exhibitor Presentations Rooms 9 and 10, San Diego Convention Center

Room 9: Sunday, February 19 9:30 AM – 11:00 AM Oroboros Instruments GmbH Mitochondrial Bioenergetics – A Quantitative Analytical and Diagnostic Approach Mitochondrial fitness is essential for brain and muscle function, for resistance against preventable and age-related degenerative diseases and therefore for quality of life. The capacity of oxidative phosphoryla tion (OXPHOS) is a fundamental part of mitochondrial fitness and a key element in bioenergetics. Comprehensive and real-time OXPHOS analysis is based on biophysical and biochemical concepts related to mitochondrial core energy metabolism. It extends bioenergetics to the level of mitochondrial physiology for functional diagnosis in health and disease. The Oroboros O2k is the state-of-the art respirometer for quantitative high-resolution respirometry (HRR) and comprehensive OXPHOS analy sis. It has the high signal stability and unrestricted flexibility of titrations suited for application of complex substrate-uncoupler-inhibitor titration (SUIT) protocols which are the basis for investigating mitochondrial pathways and respiratory control in health and disease. High resolution and precise control of oxygen concentration enable studies of mito chondrial functions under normoxia, hypoxia, and hyperoxia. With the O2k-FluoRespirometer, fluorometric assays for ROS produc tion, mitochondrial membrane potential, ATP production, and calcium uptake can be measured in real-time and simultaneously in direct conjunction with HRR. Modules for monitoring Q- and NAD-redox states and PhotoBiology are implemented in the NextGen-O2k, further extending the analytical resolution and opening new windows to study biophysical principles of bioenergetics. We will present applications of the NextGen-O2k and O2k FluoRespirometer to explore mitochondrial physiology and pathology in various types of samples and find solutions to mitochondria-associ ated diseases. Speaker Erich Gnaiger, Founder & CEO, Oroboros Instruments GmbH 11:30 AM – 1:00 PM Journal of General Physiology (JGP) PRESENTATION TITLE AND SUMMARY INCLUDED IN ADDENDUM

1:30 PM – 3:00 PM Mad City Labs Inc Open & Flexible Microscopy Systems for Combined Single Molecule Methods Eric Drier Open and flexible microscopy systems have distinct advantages for implementing novel biophysical methods. This session focuses on 3 such systems, each of which combines precision motion control with single molecule measurements. Quantification of Lipid Diffusion Dynamics on Live Cell Membranes Through Interferometric Scattering Microscopy Francesco Reina The study of single lipid dynamics on membranes requires simultane ously high localization precision and temporal resolution, a feat that few microscopy techniques are able to achieve. We show how Single Particle Tracking through Interferometric Scattering (ISCAT) microscopy has given us new insights in the compartmentalization of plasma mem brane structure, and the diffusion modes of single, gold-nanoparticle tagged lipids. The tracked lipids appear to diffuse through a “hopping” motion between compartments of nanoscopic size (100-120nm) with a probability of crossing the boundary. These results were confirmed with the use of particle diffusion simulations in a corralled, two-dimen sional plane, which also serve to estimate the “hopping” probability. A Single-Molecule View on Dynamic Chromatin Access of Epigenetic Regulatory Factors Beat Fierz The dynamic organization of the eukaryotic genome into chromatin is integral to its regulation. We develop single-molecule colocalization imaging and single-molecule FRET approaches to directly observe the dynamic architecture of chemically defined chromatin fibers. We found that local chromatin undergoes structural fluctuations on the micro- to millisecond timescale. Internal chromatin dynamics are exploited by transcription factors to invade chromatin structure. Using single molecule imaging, we recently revealed DNA access mechanisms for pioneer TFs, genome editors and centromeric proteins. Overall, our results show that compact chromatin structure hinders factor access, but mechanisms that open nucleosome contacts, including histone variants and chromatin remodeling complexes can help key factors to overcome these obstacles. Magnetic Tweezers Investigations of the Type IA Topoisom erase of Mycobacterium Smegmatis Maria Mills Type IA topoisomerases relieve torsional strain in supercoiled DNA. These enzymes work by cleaving the backbone of one strand of a DNA duplex, passing the other strand through the break, and re-ligating the DNA. We have used magnetic tweezers to characterize Mycobacterium smegmatis topoisomerase I (MsmTOP1). In addition to a conserved core domain common to all type IA topoisomerases, Mycobacteria type IA topoisomerases have unique DNA-binding C-terminal domains that are involved in passage of the second DNA strand through a protein mediated DNA gate. In separate magnetic tweezers assays, we mea sured the supercoil relaxation activity and DNA-gate dynamics of the wildtype and mutants lacking portions of the C-terminus. Our results

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